Seconding the old, trusty Gin and Tonic. Also yeah, the gin matters - but a lot of pretty cheap gins are plenty good. I straight up like Seagram's, but if you don't want to go that cheap, New Amsterdam is perfectly good.
Good rums are great, they're plenty drinkable and much cheaper than lots of other official Good, Expensive Liquors. I love Kraken - it's an unoriginal opinion, but everybody loves Kraken for a reason, it's straight-up awesome. Rum and Cokes are a good, conventional choice, and there's also the Dark n' Stormy - rum with ginger beer.
Whiskey straight is also good, I like pale, mild whiskies. I'm a southern hick, but I like corn whiskey.
Newcastle is a pretty awesome English brown beer, if you want to go that route.