During the winter I drink a lot of coffee and tea. Stock up on some flavors you like so you'll always have fun options. During the summer I always have a big pitcher of iced tea in the fridge. Not just iced black tea, but iced mint and other light refreshing teas. I switch it up so I never get tired of them. You can try putting fruit in your teas while they steep to add some sweetness and flavor complexity.
My final line of defense (in case I'm lazy and don't want to make tea or coffee) is flavored seltzer water. It's a bubbly soda alternative with no sugar but a bit of yummy fruity flavor. This stuff is just carbonated water and natural flavors. It's cheap at the grocery store. Make sure you read the ingredients, because some brands put in unnecessary junk. I buy Polar brand, which just has those two ingredients.