The boxing button is a Quality-of-Life enhancement for Nullius. It enables you to manually box or unbox any item with a quick command. No more searching through the crafting menu!
Once you research Packaging 1, the manual boxing shortcut will become available in the shortcut toolbar.
To box or unbox an item stack, click the button while you have the item stack in your cursor. It boxes or unboxes only the items held in the cursor. You can click repeatedly to do multiple stacks.