Button Upgrade — Iron Backpacks Wiki

The button upgrade adds 4 buttons to the main inventory.

[4]- Sorts all items in the backpack. By default it sorts by item ID (ascending), but you can right click the button to toggle the sorting method to alphabetized, localized item names.
[3]- Moves all items from your inventory (the 3 rows above your hotbar) to the backpack.
[2]- Moves all items from your hotbar to the backpack.
[1]- Moves all items from the backpack to your inventory.

The upgrade also adds buttons to the configurable inventory that simply allow you to clear the items in each row with a single click.

Note: All of the buttons have tooltips in-game if you are ever confused. The delay for them to appear is 1 second by default, but it can be configured to anything you wish.