ianglefinder - Not extremely precise but close enough for general carpentry or metal fabbin to a solid degree.
mirror - bad ass when doing tight or hidden mechanic work if the phone fits in there.
dual level - best for finding a flat surface
iseismometer - I use this along with duct tape to determine shakes when troubleshooting a vehicle. It's purpose is to distinguish where something is shaking and in what direction. It records.
GPS Phone Tracker - I use the wife's phone to figure out if I laid my dead phone down at the shop or at the house. Plus in case it ever gets stolen again. Could kick my ass for not having this sooner when that happened.
Guitar Tuna - Another great when away from my tuner.