Honestly - once you have the right gear and the right situation, you woudl use it all the time!
* Air compressors for blowing up mattresses, rubber rafts, tires, etc..
* Magnetic lights, working lamps..
* AC/DC Transformer for plugging in a laptop or something while sitting in the bed of your truck.
Lots of little uses that once you find, youll always use!
I'm going to be ordering up a good chunk of stuff from Del-City this summer perhaps, getting a large fuse block for the engine bay, and planning on wiring up 2 12v outlets with on/off rubber weather switches for them. Right at the stake pocket holes =)
Just ordered up 2 of these:
and a few inline fuses for them.. pretty cheap :-)