First suggestion:
I saw a comment on this mod's Curseforge page that gave me an idea. There are lots of mods that add sleeping bags; people may prefer the ones from other mods for reasons such as cosmetics (appearance) or functionality. Since it would be difficult to support every sleeping bag mod, I suggest making a sleeping bag "slot", with a configuration line that lets you add entries for every sleeping bag item you want to use with this mod- probably with some mods already supported. (This could be part of Traveler's Backpack Integration.)
Second suggestion:
Expandable storage! I like the ability to configure how much the backpack holds, but for players like me who like things more or less balanced, (configurable) expandable storage would be great. You could make it so that every upgrade requires the same materials, or make it more expensive the more time you upgrade.
What I'm imagining (though I have no idea how hard it would be to code) is for there to be "tiers" and "levels" of backpacks. When you make a backpack of any tier, it starts at level 1. Then as you upgrade it, it goes from level 1 to level 2, then level 2 to level 3, and so on, until you hit the maximum for that tier, let's say level 10 for tier 1. You wouldn't be able to upgrade that backpack anymore, then, except with non-storage upgrades. (The tooltips would say something like, "Storage Tier 1", then under that "Storage Level 1".) A backpack of a higher tier wouldn't have any extra storage at level 1, but it would be able to be upgraded to a higher level than a lower tier. So a tier 2 backpack could be upgraded to level 20, for example. And users would be able to configure 1. how many slots each level upgrade adds, 2. how many levels each tier has, and 3. how many tiers there are.
That's just my idea; even a simple way to upgrade storage would be satisfactory to me.
I'm very excited to try this mod; I've been wanting an all-in-one backpack mod that lets you wear both it and your chest plate, so I was very excited when I found it! Thanks for all your hard work!