Calf raises! Do one set of 50 while brushing your teeth, or 20 while sud-sing your hair in the shower, or 2 sets while doing the dishes.
If you are unaware of what a calf raise is, its exactly as it sounds. Standing up, you raise your body up, to where you're only standing on your toes. Preventing yourself from going complete flat footed before doing another rep will keep your muscles tightened, working them more!
