Post yer roadside repair tips and tricks here.
Here's one of mine to start:

Problem: Forgot to bring the headlight mounting bracket with me for the night portion of commute.
Solution: I put the headlight up against side of the drop section of drop bar and taped it in place. Rode the whole way in the dark and held very tightly - no vibration. It is a miNewt.600, cylindrical/tube shaped headlight. So should work for any tube/flashlight shaped light.