I normally carry:
Ambien: If I just want to sleep, several hours. Period.
Valium: For high-anxiety situations like long, uncomfortable flights on LCC's and for turbulence.
Dramamine: If turbulence is expected and if I don't want the additional drowsiness I get from Valium.
Benadryl: If I'm fighting allergies and want to get sleepy onboard.
I've pretty much stopped using Ambien due to its high cost, and because I really prefer to stay awake during long flights, esp. since I've been fortunate enough to fly lots of first class lately.