Strong fine pointed tweezers.
Circlip pliers
Very fine pointed pliers.
Wire cutters that don't snap when force is applied.
Wire stripping tool - teeth are the usual field expedient for this.
I find haemostats incredibly useful. May be called locking tweezers. No point in buying expensive surgical grade ones though.
A small vice - or in the US vise.
Cleared space to work. I work on top of a large sheet of paper (A3/11x17") which makes it much harder to lose small parts. I still manage anyway.
An old ceramic tile for soldering on.
Desoldering braid. Cheap and handy for lowering resistance.
A few feet of solid core Cat3/4/5/6 (It doesn't have to be fancy, and Cat3 has less twist so is easier to part out) ethernet cable. If you have the Ultrafire C3 habit I have, a strand of copper from this stuff is invaluable for forcing the parts to make electrical contact with each other. I think I own about 400m of the stuff left over from network wiring jobs.
In extreme cases a metre long Stilson wrench can come in handy.