How to open backpack/add things to packpack

[Jos]

I got a backpack but I dont know how to put things in it or check its inventory. Also my friend im playing with didnt get backpack can only one person have one?

[Pyllymylly]

You can probably only have one backpack.

You can add things to it by either hovering the item and touching the backpack with it. Or equip the item, aim at the backpack and press 4 to "Put item" into it.

You can take items from it by aiming at it and selecting the correct number for "Open" (3?).

[Hippiecab]

One key step is that you need to drop the backpack by holding E with empty hands, then you can interact with it.