I used to work for an operation that used diesel (Thielert) engined 172s, and as such the wing tanks had to be absolutely airtight, so they were installed with the 'flip up' and twist type fuel caps which, if you've ever used them, you will know how tight they can be to, well, flip up! Especially in the cold morning!
So it became routine for me to climb up, pull out my car keys, use them to lever the catch up, lay them next to the hole (too lazy to put back in my pocket immediately), etc etc.
Heh... It was about 7 hours later one day, after 3 separate flights around the country, and after landing and going to my car that I realised they weren't in me pocket!
It was a grass strip... With about 1.5 miles of grass (some of it long) taxiway in total...
