These categories are Equipment, Mission Items, Misc, Crafting, and Consumables.
The backpack window can be switched in size between a 10 and a 5 row display.
To delete an item, drag'n'drop it to the Trash Can icon with the down arrow in the lower right corner of the backpack window.
To change the category of items displayed click on the corresponding tabs on the right hand side of the backpack window.
For transfer of items or credits to or from the footlocker, see: AFS Issued Footlocker