You have to use paper clips to help keep your eyes open at 4 am on the final leg of the night...
You keep your ice chains for your shoes on while walking on ice covered wings after landings....
Someone on the radio starts singing 'in the dead of the night' at 2 am...
You try to find a hotel to go to bed to and find out that all the rooms are booked, so you go back to your aircraft and sleep in the cockpit... <did that one way too many times in the Baron and Bonanzas>