What’s Your Favorite Inventory System? Let Us Know, Down Below!

I've never had a problem with encumbrance. I just put everything on my horse then put my horse in my horse pocket.
😀

I'd argue that to what degree you simulate  logistics is one of the most important design decisions. It has a massive effect on every pillar of a game and can drastically alter what type of game it becomes.

One thing I think is absolutely criminal is that, for systems that do use straight up weight-based carrying capacity, they never have a big, top-level line on the inventory section of the character sheet for "total weight". A huge part of the headache in those systems is that when the question of "can I carry this?" comes up, the answer requires going through your entire list to total things up, at the moment. It's like if, instead of having your HP total written down and updating it whenever you take or heal damage, you wrote down each instance of damage and healing and had to add all that up on the spot to find out your current HP. Treating carrying capacity more like HP, with your total weight calculated when you set up your loadout and updated on the (actually fairly infrequent) occasions you pick up or use/lose something would surely make it far less cumbersome to track.
Perhaps still not as easy as slot-based inventory (which I generally lean toward preferring), but if you're playing D&D or another system with carry weight, do yourself a favor and write a big ol' "total weight" line at the top of your inventory section. Because for some bizarre reason, the publishers of those systems never seem to do it for you.

My favorite is Mouseguard, which is you can carry whatever you can draw on your character

When gold pieces were XP the inventory system was called Henchmen and Hirelings.

Carrying capacity is the limit.
Encumbrance is the penalty or condition caused by approaching or exceeding that limit.
Simple version:
Carrying capacity answers: “How much can I carry?”
Encumbrance answers: “What happens when I carry too much?”

Practical TTRPG version:
A character might have a carrying capacity of 10 slots. They can carry up to 10 slots normally. At 11–15 slots, they are encumbered: slower, noisier, worse at climbing, worse at fighting, or easier to exhaust. Above that, they may be overloaded and unable to travel effectively.

Design distinction:
Carrying capacity is usually a measurement system.
Encumbrance is usually a consequence system.

Inventory slots and AD&D gold = XP solve different parts of the same old-school design problem.
Inventory slots create logistical pressure.
Gold = XP creates player motivation.

Together, they turn treasure into a real game decision.
Simple distinction
Inventory slots are a constraint.
They limit what characters can carry.
Gold = XP is an incentive.
It tells players what the game is really about.

So:
Slots make treasure heavy.
Gold = XP makes treasure matter.

The big behavioral difference
Modern combat XP teaches players:
Fight things to advance.

Gold = XP teaches players:
Get value out of danger and survive.

Inventory slots then add:
You cannot take everything. Choose.

That changes the table culture dramatically. Players start caring about carts, sacks, hirelings, mules, secret exits, portable wealth, gems, jewelry, maps, and safe retreat routes.

I kind of like an idea I first came across in MCDM's next game, Crows (it's not out yet obviously but James Introcasso talked about the inventory system in a Patreon post), but I've heard other OSR games have done something similar before. You have some slots on your body (hands, neck, belt, boots etc), and then your backpack has 10 numbered slots. To retrieve an item from your backpack, you need to roll the number of the slot it's in or less on a d10. If you fail, you can spend the round rearranging your backpack instead. It's especially important because Crows has no classes, many of your abilities instead come from equipment, so you may need to dig out that spellbook to be able to cast the spell you need right now!

Video games helped improve my system, despite the common differences in experience: Each PC has a limit of: 6 different pieces of equipment worn,
3 consumables (potions, scrolls, special arrow bundle, etc),
and 3 of any other items.

I used a homebrew thing in one of my D&D games where people had a gear usage die like Forbidden Lands or the black hack. They roll it for like setting up camp and toruches, but if they needed something very specific like a grappling hook,, they can downgrade their die size.  I paired it with a slot inventory system so you where instivied to plan ahead, but if you really needed something, you had a way to Schrodinger's it from your pack as long as you had a gear die.

In the TTRPG called Exalted they only care about important items that go onto your person. The mundane items that your character uses is determined by your skills. If you have points in sailing then you can pull out sailing type items like maps and spyglasses or whatnot. It's up to the DM to determine if you have it. It's similar to Schrodingers Inventory.

Stormland, a vr game, has that idea of slots on the front of the body. You can look down and grab a grenade or something off your body or reach down for a gun or reach to your back for a weapon.

“Look em’ up buddy” dropping that wisdom

I love exploring the cross-section of Inventory with all the other facets of gameplay, which is why I went with Inventory Slots for the system im designing.

Inventory Slots in this system represent not only your equipment you might have, but can also be occupied by Wounds and Fatigue - limiting how much you're able to carry while remaining effective.

I went with a Classless design, emphasizing that your character "build" is what you choose to bring with you; your equipment determines what you are capable of doing. Thieves tools? You can pick locks. Healers kit? You can patch up wounds.

Casting Spells gives you a slot of Fatigue, which puts a hard limit on the number of spells that can be spammed before the caster requires a rest.

For each character, taking damage results in a WOUND being created, which also takes up an inventory Slot. Accumulate enough Wounds, and your character begins dying.

The Pathfinder 1e prestige class the Chronicler that has a fun feature called Deep Pockets. They can spend a few hours shopping in a city and spend 100gp per level to buy generic gear.  While adventuring, they can decide what they bought as long as it fits in a backpack.  So you can have had miraculously bought the exact potion or scroll that solves whatever problem you are facing.

Also, hiding a Draw Steel correction below the main comment in that they got rid of magic kits during testplay. Now only Martials get kits.  But the core idea is the same with your Kit making you the Legolas archer, the Conan reaver, or the Lancelot knight.

Just had an idea after watching this.

An inventory where you have that Tetris items that you can put* on your slots, but you make the pieces white boards so you can write what they are on them. You can buy adhesive white boards paper anywhere on-line and glue them on wood or something.

It gives that tactile sensation while keeping things clear and reusable. Just make differently sized squares and rectangles and you're good to go.

For legendary items, make them out of metal. For potions you can try ceramic.

I like the idea of connecting your inventory to your character. A system where your backstory influences your non-combat inventory sounds right. A bit like packs or loadouts and quantum inventory mixed together. Pick a couple general categories related to jobs, hobbies, and habits and you can pull out any item you need if it fits in those categories.

All mechanical items (like weapons, armor, consumables, etc.) have a weight from 1-6, and you can carry twice your strength stat. Low-strength characters are rather limited in what they can carry around.
All flavor items and crafting materials are free as long as you have a bag item. Every player has an item called "equipment" which represents everything they need to use abilities, and skills, ammo, and general adventuring gear. If the GM is unsure if something is part of their equipment, they can make a skill check to see if they have the item.

This is a nice mix of most systems you mentioned. It keeps it loose, so it works for different settings, and the math that you need to use is very simple.

I like to make inventory management only an issue on journeys longer than a week and even then I like to focus on space over weight.
Because either it's something negligible, something that might fill a pocket, something you need a backpack for, or something you can carry in one hand or two hands. Then I can just say the cart carries 4 crates that can be lifted with two hands and each crate can hold up to 2 backpacks. Everyone is familiar enough to understand what might fit in a backpack, at least in my experience.

Slot based inventory is my favourite way for games that care about the logistics game to handle inventory (bonus points if the slot based inventory is represented by a grid that tiles representing items, conditions, etc, get put into. Mausritter has my favourite inventory system I've encountered so far), though 90% of what I play and run don't give a toss about that.

I do enjoy 'determine it as you need it' stuff like FitD games use, mind.

Mausritter also does the Resi 4 attache case thing on top of having specific paw, body, and pack slots, while not allowing you to rotate items that are more than one slot, so if it's horizontal, as one of the armor slots are (the one with the shield, so it takes up both your body and your off paw slot), you wouldn't then be able to fit it into your pack if you've got a 2x2 item in there, which I've encountered a couple of times in my current campaign. There's also Flail - on Backerkit atm - that's doing that as well, which is by one of the Mausritter designers and being published by the Mausritter publisher (Though this is the least interesting thing it's doing, the combat that game has is wild )

One tabletop RPG I really like for inventory is Within the Ring of Fire. Every item your character has is always considered to have on that character as long as it makes sense. The only item that ya kinda don’t is your weapon. That must be written down on your character sheet.