And why I think it's good

To me, the OSR means going back and making dungeon crawls fun again. I think, back in the day, dungeons were THE THIING for a long while, and they got played-out, so games and gamers drifted away. But the OSR pulls us back. "Let's make the dungeon crawl cool and fun again", says the OSR to me.

Being in a dungeon, ultimately, would suck. If we're gonna have a good time, we need to embrace that suck. But we need to make sure it doesn't suck for us, the players. So we design gamey things to turn chores into good times. Inventory management is notoriously a chore.

Inventory slots are a good solution, but I like to know where stuff is, as the player and the GM too. In a dungeon crawler, your stuff should be important. Humans lug tools and gear around for a reason - it makes doing impossible things possible. An adventurer's gear, therefore, should be something we pay attention to, not handwave away or replace with superpowers.

And also, it's always bothered me to write down "backpack" in a slot. Don't the things in the other slots go inside of the backpack? Does the backpack count as an item when it's allowing you to carry so much extra stuff? It's never been clear if you need a backpack at all.

And how does the game treat your inventory differently if you don't have a backpack? Does the GM now need to remember if you do or don't have a bag to keep your stuff in, and must they figure out some way to reward those with bags or penalize those without?

Blah blah blah.

Here's the inventory system I came up with for Pitfalls & Pathways.

Inventory

A PC can hold one item in each hand. These are your mainhand and offhand slots. These can be heavy or very heavy items (usually very heavy items require both hands).

You can wear 3 items on your person in outfitting slots. These are your clothes and other attire. These can be heavy or very heavy.

You can carry up to 3 items in accoutrement slots. These items are attached to your person by way of straps, twine, buckles, pockets, etc. These can be heavy, but not very heavy (without class ability).

Three trinket slots can accommodate small items you wear like jewelry, rings, necklaces, bracelets, etc.

Three pocket slots can hold small, loose items like coins, keys, vials, parchments, etc.

A bag holds 5 items. While empty, the bag can be stored as an item. When holding items, the bag must be held in a free hand slot. Check the box if you have a bag that contains items. It becomes heavy when full or it can carry a single heavy item.

A backpack holds 10 items. Check the box if you have one. It becomes heavy when holding 5+ items and very heavy when full. It can instead carry two heavy items or a single very heavy item. Backpacks are affixed to a PC’s back and must be stored in an accoutrement slot.

☠ Pouches are used to hold bunches of tiny items (like coins or caltrops) or piles of fine substance (like powders or sand). A pouch counts as a single item and takes one slot.

A quiver holds a bundle of arrows or quarrels. The quiver and its contents are count as a single item, typically stored as accoutrement.

Encumbrance

PCs can carry a number of heavy items equal to 1+Strength (min 1).

Very heavy items count as two heavy items. Generally, five normal items are heavy and ten normal items are very heavy.

If a PC carries an additional heavy item over their limit, they gain the encumbered condition. A PC may not carry more than one extra heavy item. The encumbered condition applies a penalty to movement and dexterity checks.

Bulky, large, or awkwardly-shaped items may be considered heavy or very heavy for simplicity.

The "heavy items" mechanic is inspired by Kirin Robinson's Old-School Hack. Ben Milton's Knave reminded me about slots. Slots-as-locations are inspired by Thor Olavsrud's Torchbearer, with confirmation by genius Idiomdrottning and her inventory system.