Flight attendants aren't bartenders, so if you want something more complicated than a rum and Coke, you better know which ingredients to ask for.  Here's a list from "Esquire" magazine of four cocktails you can make on a plane . . .

#1.)  A BRANDY, RUM, OR WHISKEY SOUR.  You just need the liquor, the ice, a packet of sugar, and some lemon juice.  You can get THAT from the lemon wedges they use for hot tea.

#2.)  A TOM COLLINS.  You need gin, sugar, lemon juice, club soda, and ice, which are all available in the beverage cart.

#3.)  A WHITE RUSSIAN.  Add two parts vodka and one part Kahlua to a cup of ice.  Then for the cream, either use milk or half-and-half.
The only downside . . . assuming your flight even HAS Kahlua . . .  is if there's a two-drink limit.  Because if the flight attendants are strict about it, they might not give you more than two little bottles of liquor during the flight.

And since a White Russian has vodka AND Kahlua, you might have to use BOTH of your drinks to make ONE cocktail.
#4.)  A PRESBYTERIAN.  "Esquire" says you should try this one first.  It's equal parts Scotch and ginger ale over ice . . . and apparently it's better than it sounds. 

(Esquire.com)