So, I've been trying to make a backpack...

How would you make a backpack, exactly? I want it so that if you pick up an item that's in the backpack, it'll get sucked into the backpack. Is there a way to check what item you picked up, then move it into the backpack?

Also, would there be a way to make it auto-craft when it gets in there? Like, if I had an item in there that says "If you can, use items to craft this!"?

Thanks!

Sincerely, Wub

You need to start somewhere else.  All of those things are fairly advanced operations.

You can start by creating an item that stores an inventory.

 

Then you can subscribe to the Forge ItemPickupEvent, check if your player has your backpack item, and store the item in there instead of the regular inventory.

 

For crafting, you'd probably have to implement that in the Item class onUpdate method for your Backpack Item, checking its inventory every now and again to see if there is anything it can craft.