You may be aware of the somewhat cult reputation for 7/11's and convenience stores in Japan. They're notorious for being a haven for nearly any you could imagine, food, hygiene, or otherwise. Some Family Marts are even opening up gyms at certain locations.
Imagine a nice gas station (without the gas), that actually serves good ready-to-eat or take home foor ranging from sushi, to tonkatsu, and just about every Japanese food in between. Too bad people in Japan aren't familiar with weed because conbinis would be the stoner's god sent dream. 7/11, Lawson, Family Mart, and Mini Stop are among some of the most popular conbini chains in Japan, each has its own unique feel to it, but all essentially serve the same purpose of helping you get whatever the hell you need.
An excellent place to shop for groceries and food for wherever you're staying as well. Cheap cartons of all types of tea, and orange juice, hot food including dumplings, and fucking amazing fried pieces of chicken. A couple of these after drinking 8 overpriced Japanese beers is a live saver.
Pretty much any food we got at any convenience store was good and well worth the price. Onigiri [おにぎり] are a great in between meals, and come in a variety of flavors. Tonkatsu pork dishes, curry, dumplings, instant ramen, and more Japanese cuisine can be found in droves at every conbini. Like I said though, I highly recommend any of the fried chicken, fucking incredible.
Did you forget something at home when you were packing? Don't even fucking fret, just find the nearest conbini and grab whatever you need. I didn't bring a single hygiene item with me, planning on pickin them up at a Seven Eleven, and right next to our Shiomkitazawa Airbnb was a Lawson's, open 24/7. I grabbed a tooth brush/toothpaste travel kit which was incredibly perfect, bottles of shampoo and conditioner, and deodorant, all for around 1000¥, which was way better than fucking with bringing my own.
Conbinis are also famous for their hangover remedies. As told by an Australian to us at a sake bar in Kyoto, drinking one of those before getting fucked up and you're "mint" the next day, as he said it. I drank one the day of being a little hungover and I do think it helped, plus it ws lemon flavored, which I couldn't get enough of in Japan.
Alcohol is sold at conbini's too, ranging from cold beers and highballs (these are gross, but quick ways to get you drunk), to sake, and plenty of familiar American whisky and other liquor. If you want to carry a little traveler with you, look for the nearest conbini.
The range of non-alcoholic drinks is astounding, as well. Smoothies, flavored teas, coffee, seemingly everything that you could ask for. It's even common at these stores to have a section of hot canned drinks. Tea and coffee such as Boss and others can also be taken from an already hot rack of drinks...some vending machines across Japan have hot drinks as well.
Even household items or often forgotten/ruined clothing items. Any kind of electronics charger, office item, memory card...all available and more. Forget a tie? Conbini. Feel like you're still drunk on the way to work? Conbini. Want to indulge yourself in cheap but delicious Japanese cuisine? Conbini.
Conbinis also have English capable ATM's, and most don't charge more than a $1 fee (depending on your bank, as well.) Japan is still much a cash driven society, so expect to be carrying a lot of cash on you at once, and conbinis are a reliable place for easy cash. Fair warning, most ATM's require a minimum withdrawl of ¥10000.
You can even forward your luggage to your next lodging or airport from some stores, something in hindsight I wish we would've done. Along with even more things such as shipping packages, making copies, and getting items notarized, conbinis look to be something that Japanese neighborhoods and livelihood truly appreciate.
What I think it similar to the bodega in New York City, another sign of a city's natural ability to provide for itself and the productivity and flow of its citizens. Midwesterners and roadtrippers will know, every time you walk into a conbini, it's like walking into an incredibly nice truck stop, but instead of white trash and rednecks working (not fair to generalize, I know), it's upstanding and positive people who buy into Japan's productivity. An absolute product of Japan's undying respect for itself as a country and it's society as a culture.
12/2/17: One of my favorite clothing brands, Chinatown Market, even put out a small belt collection featuring 7/11 and Family Mart, but where the fuck is Lawson?!