7-Eleven, Lawson, and FamilyMart sell genuinely delicious sushi, sandwiches, onigiri, hot foods, and desserts at fair prices.
FamilyMart's chicken (Famichiki) is iconic. 7-Eleven's egg sandwich (tamago sando) is legendary. Lawson's premium roll cake is a dessert standard.
These stores also have international ATMs that accept foreign cards (look for the international logo on the machine).