Almost no matter how empty your cabinet or fridge is, you can make a tasty cocktail, if you know the basic 3-2-1 principle. Even if you don't like whiskey or cognac you can make a nice whiskey sour just using whiskey, lemon and sugar or anything similarly sour and sweet respectively.
During my time as a hedge fund manager, I was often invited (by commission hungry brokers) to various wine and champagne tastings.
A couple of times we even ventured into the land of cocktail tasting (and mixing). Here are a few hints and tips on cocktails made easy, that I took away from those.
1. Make your own syrup by bringing 1 liter of water and 1 liter of sugar to a boil. Let it simmer until the syrup is clear.
Put it outside to cool before pouring it into a PET bottle.
That should be enough for about a hundred drinks. It will keep well in the refrigerator for a year if you and your friends don't finish the whole batch tonight.
The simplest good, strong and tasty 6cl cocktail is made from 6 cl liquor, 4cl lemon juice and 2 cl syrup. The rest is just variations and tweaks of that basic recipe.
Take 3 parts bourbon (Jack Daniel's), 2 parts lemon juice and 1 part syrup. Shake with ice and pour without the ice. That's it. Add ice cubes and/or Angostura bitter if you want.
3 parts cognac (VS), 2 parts lemon juice, 1 part triple sec or cointreau (or blue curacao for color, it's the same thing as triple sec and cointreau). Shake in ice.
Crush a whole lime sliced into wedges, crush 10 leaves of fresh mint, mix with 6cl of dark rum (not too dark and full) and 1.5cl syrup. Pour in a high glass filled with ice cubes and top off with anything bubbly, e.g. club soda or champagne.
Mix and shake like hell and serve including all the ice.
You can make it on ordinary triple sec or Cointreau instead of Blue Curacao, and the Angostura is just to make it more adult. Some (a.k.a. girlie girls) like to add a few parts of lemon soda as well.
Remember that 2-step "cowboy" drinks like Gin & Tonic, Vodka & Red Bull, Rum & Coke etc don't take into account basic gastronomical insights regarding which balance of flavors is palatable.
Be better than that, more refined. Or do you serve hot dogs for New Year's dinner as well? Don't be that guy.
If the bartender has no idea what he's doing, go ahead and order a GT, but otherwise; just say NO.