Hiro A H R: All time favorite. Compact supermarket but they got everything you need in heart of hiroo and roppongi area. They have dog parking area as well.
Jon Steinback: Go to any 7-11 or AM/PM or anything and get onigiri balls (they're 100 yen (~$1) and delicious, fresh, and ingeniously packaged). And try a new strange drink every day you're there.