zero gravity chocolate
I can remember once conducting a cross country flight (probably back from an aerobatic competition, I can't quite remember) where I'd deemed it a nice idea to stow a mid-flight emergency snack in my secure, zip-up cockpit bag from which nothing can fall out mid maneuver (I fly a Pitts S1S and do very little other than aerobatic flying). This had been a great idea, except as it happened I never quite felt the urge to eat it, hence in the bag it stayed.
You can probably see where this is going...
On the cross country flight I'd not had the zip up bag zipped up as I'd been using the chart on and off and trying to unzip the bag one handed is a complete pain in the butt. It was a completely uneventful trip. My next flight a few days later was for a training sortie - I think if I remember rightly I was flying the BAeA Intermediate Known sequence or something similar, anyway, off I trundled up to 2500', wing rocked and I was away. I remember I was flying a really nice sequence until I got to something that involved a push to about -3g and all of a sudden I heard something bang, hard.
Feeling somewhat concerned at this point I very rapidly righted the little Pitts and wondered what on earth had come loose. A quick glance revealed that I'd somehow managed to leave the bag unzipped (lesson 1 learned - ALWAYS check the bag is done up), so now I knew that I had a loose article somewhere in the aeroplane. I couldn't see anything anywhere so there was nothing for it but to invert the aeroplane and see what dropped up into the canopy. Of course nothing did - the offending item was obviously stuck under the seat at this point, or worse - down the tail somewhere. So there I was, upside down, feeling like a bit of a lemon, jiggling the aeroplane back and forth until finally, a particularly forceful inverted jiggle released said article...
I was then unceremoniously smacked in the face by a floating Snickers bar.
The main lesson for me really was one of conducting more rigorous checks of the little things before flight. Loose articles can kill or at least leave a bruise ;-)