I'l be travelling in a months time and my doctor has prescribed me Valium (diazepam), for anxiety as well as Ambien (zolpidem) for sleep. He said that combining them with alcohol isn't advisable but not bad so long as I don't take too much.
I've heard from other people that combining prescription meds and alcohol is illegal on planes but other sources say that it's only illegal if your become and intoxicated and then your behavior endangers the passengers and crew.