Small items I'd imagine is flint, knives, arrow heads, linen, etc, etc. There's plenty of small items in the game. Take the item into your hand, think of how it would weigh or fit into something and you can find so many of the things in the game that'd be considered small. And not like obvious things that aren't small like rocks. I've already listed a good bit as is, gears and temp gears are more examples if you're looking for more. Looking in the game is better.
I definitely like the idea of belt bags, I thought about this myself before. Maybe something that can be done.