Written and submitted by DS.Poker, this script simplifies the use of backpacks and the repair pack in particular. A keypress (the spacebar by default) activates the current pack. If that happens to be the repair pack, and an object is eligible for repair (in your sights and close enough, as normal), the repair pack remains on, repairing the object. You won't need to hold the key down. When the object is repaired (or you move away) the weapon you were previously using is automatically brought back, ready for use. If you press and release the fire button (assumed to be the left mouse button), any repair activity is stopped and the previous weapon is automatically brought back. This script also works for self-repair.
That may sound confusing, but trust me, it is easier to use than describe. Just give it a try. I consider this an invaluable script and have added it to my own setup.
Update: Poker has adapted a version of this script to use Writer's Support Pack (he's had quite a few requests for this). It is listed as a separate download, below. You will need to have installed Writer's Support Pack and the PrestoPack v0.93 for this version to work properly.