Solid Aisles Dedicated to Cup Noodles
I've backpacked several countries before, and during that time cup noodles saved the day on many occasions. They're cheap, convenient and tasty - but it helps to have a bit of a flavor selection so that you don't get bored eating noodles on the regular. Head to any Japanese supermarket and you'll find an incredible range of cup noodles in different flavors, with different noodle types and different add-ins.
Loads and loads of sweet treats
Fun finds at every turn
Wine in juice box containers (for little more than a dollar!)
Feel like a glass of wine to cap off a fun day of sightseeing, but you don't want to buy an entire bottle because you've got a shinkansen to catch the next morning? Well - juice box sized wine is something you can find at the supermarket here. They had both red and white wine, if you have a preference - or maybe you want to give both a whirl!
Grab and go taiyaki, nikuman, American dogs and more
These were priced at 48 yen each, and there were containers provided for you to just pick and mix whatever you'd like - they count it up and charge you for it at the register. If you've got a microwave or toaster oven where you're staying (perfect if you're at an AirBnB with a full kitchen setup!) then a few of these could make you a meal and dessert for next to nothing. Also yes - corn dogs are called American Dogs in Japan!
Sushi at wallet friendly prices
One of the best things about Japanese supermarkets is how incredible their pre-prepared food sections are. There are tons of options for meals that you can take back to your accommodation to heat and eat - but they also have awesome trays of sushi that you can enjoy right then and there. They provide eating utensils too, so if you pop in to a supermarket you can head straight onto a park and have an impromptu picnic if you'd like!
This is just a glimpse into some of the things at my local supermarket, but they really can be a traveler's best friend - check them out if you have a chance!