Backpacks could use up one of your three “at hand” slots to make them less of a non-choice.
I don’t think I understand “non-choice” here? Backpacks seem to be an “always choose” option? I think two slots is too small however.
Right, exactly. By non-choice I think I mean the same thing as your “always choice”. That is to say it’s something everyone will want to get if they have the gold because it really has no cost.
What I’m proposing by having it take up an “at-hand” slot is to make it an interesting choice. You can choose to maximize for carrying weapons/shields or for carrying gear/treasure by whether or not you bring a backpack.
While i do not agree on having the backpack in the "at-hand" slot (I think that would be awkward to use), i can agree that the backpack might be too good as is (I can understand it is their in case your playing a low STR character. Having only 4 inventory slots is VERY limited).
What i would choose to do is instead would be to remove the backpack, make an "Container" slot on your character sheet, which you can carry one kind of "container" that gives you some benefit to your inventory. This could include Quivers and Slingstone pouches, but if i where to spitball some other ideas i would say:
Leather Satchel: Your carry capacity is increased by 1.
Coin Purse: You can carry up too 200 coins of any coinage without them counting as an item.
Waterskin: You can carry within this up to 3 units of liquid without it counting as an item.
Lamphook: You can attach a Lantern or Oil Lamp, making you able to carry it without using one of your hands.
Medicine bag: You can carry two items out of the Medicin category without it counting as an item.