If I'm alone, I usually let out whatever farts I have in store. Partially to avoid identifiably stink up the office around my coworkers, and partially as a gift to the next person taking the elevator.
I rarely travel more than a couple of floors. It's a small building, so chances of being intercepted are low. Besides, I can always pretend like nothing; Remember the famous Benjamin Franklin quote: "He who smelt it dealt it"
Personally, I'd get lost in my mind.
I like puzzles, so how about Simon Tatham's Puzzles, website, IOS app port, Android app port
One of my daily puzzle is domino fit, but that might not be enough for the day.