Drinks tend to water down quickly in the summer heat, but flavored ice cubes can always make a cocktail exciting. To make a passion fruit and basil cube, mix juice with chopped fresh basil. Serve with seltzer for the non-alcohol-drinkers. A ginger and honey cube can be made with equal parts water, honey, and grated ginger. It works best with a vodka tonic, like our salted plum version.