Add special slots for backpacks with trinkets API https://github.com/emilyploszaj/trinkets

I think adding this compatibility by making a special belt that only appears if trinkets or curios is installed could work if that is possible. Have it be an 18-slot inventory that fits on the belt slot and has a recipe similar to the camping pack.

Perhaps also give it a separate keybind in case someone wants to wear a backpack in the regular chest slot as well. That way people could have some extra storage without losing armor for tools and such, but if they really want more they can make that choice too.

While we're talking about OP shulkers as well, you might want to black list them from being placed inside your backpacks if they aren't already.

Trinkets support would be cool, alongside a setting in the config. Then everyone's happy.

Added in 3.0.0

I agree that this would be an excellent decision - backpacks are nice, but often times I'd prefer a chestplate, especially on hard mode!

We have debated something like this and are reluctant to in light of balancing. We don't want to add an OP backpack to the game to conflict with shulker boxes as a progression milestone. The idea of a backpack in this mod is to be a utility to carry more while traveling, not just to be an exploit in carrying more items for the sake of it. I agree though that a chest plate would be kind of nice at times, we may have to talk about it again.

I do agree that it would undermine the utility of shulker boxes - perhaps an alternate backpack created with shulker boxes could be made and slotted into a trinket backpack slot? Or combining a backpack with a shulker box makes it into a trinket form?

Not sure I see the problem here. Using trinkets could be optional, and players still have to make a choice between the backpack, elytra, and whatever any other mod adds. I don't think this would undermine shulker boxes at all, as shulker boxes enable vastly more storage than a single backpack could ever allow (and are honestly pretty op IMO).

Curious shulker boxes would also be a good mod to use for this. someone using it would already be using shulkers as a backpack

I mean, wearing an elytra is supposed to come with the tradeoff of losing out on the breastplate slot's protection, but Trinkets breaks that by letting them both be equipped. It seems to have its own ideas about balance to begin with.

I agree with this idea. Even if it's a config option that's off by default!
Trinkets adds more slots specifically so you can wear armour and other items at the same time, that's literally the point of the mod. Adding support would still make you choose 2 out of:
Backpack, Elytra, Chestplate, Misc. Back Trinket
so there's still a tradeoff for sure!
And it's still not nearly as powerful as Shulker Boxes, as it adds only 1 extra inventory: you can't fill your inventory up with full backpacks like you can with Shulker Boxes!