Backpack_newideas!

You can craft it at a workbench using three strings in each of the left and right vertical columns, and three bundles arranged vertically in the center column. You can open it directly from your inventory, just like a bundle.

There are other ideas as well, though the crafting steps differ slightly.

It's 5 slots.

It is more convenient than a Shulker Box, but its storage capacity isn't particularly large.

You can create a larger backpack by combining three ordinary backpacks.

It is useful from the early to mid-game, and since it opens faster than a Shulker Box, it is likely useful in the late game as well.

Also, the color of the backpack is determined by the color of the bundle used to craft it, and even after it's made into a backpack, you can change the color by using two dyes (since it's large)!
It would feel natural to be able to change the color using a cauldron, too.