Rum is the classic choice for a reason, specifically a good aged dark rum or a standard white rum, which pairs wonderfully with the caramel notes in Coca-Cola.
However, if you want to branch out, a quality bourbon or Tennessee whiskey makes an exceptional mix, often referred to as a classic Kentucky and coke. For a lighter, more refreshing twist, you can also try a splash of lime juice to brighten up the sweetness. Since you are looking for something low effort, sticking to a standard rum and coke with a squeeze of fresh lime is probably your best bet for tonight.