I saw or read a Martha thing a few years ago about cubing watermelon and freezing it on a sheet of parchment on a cookie sheet to make watermelon ice cubes for drinks. Of course I tried it and it was fantastic. Particularly in vodka lemonades (or just lemonades in general).
I cubed up a small watermelon a few days ago, and I'm having the annual 'I'm obsessed with summer and watermelon eating' thing . So, Martha whispered in my ear, "let's freeze it, it will be another way we can eat it all the damn time". I left about 1/2 of what was left (maybe 3-4 cups) in the fridge, and laid out the rest in one layer covering the bottom of a metal 9x12 parchment lined baking sheet, and put it in the freezer
After work (about 10 hours later), we put the fridge watermelon in the blender and pureed until it was nearly liquified. I added the frozen watermelon cubes in batches, and voila! Watermelon slushes! They were icy, super sweet (almost too much so for me, but I still had no trouble finishing it) and probably about 100 calories (let's not talk about natural sugar).
I think this would be great as a cocktail (not sure what would be the proper poison- vodka, rum or tequila), maybe a little basil as well. In the interim, this was way fast and easy and a fantastic hot summer night treat!