One time I was biking to campus and I saw the bus so I decided to take the bus the rest of the way. The bus stopped for me and I put my bike on the bus's bike rack then I climbed on the bus. It was only a mile or two but I watched as my bike headlight loosened and swung freely then fell off into the street.

I think the trick is to make a point of tightening the screws every so often.