First time to Japan ? Went to a konbini (convinience store) and had no idea what to buy or what the cashier said ? Me too I was in the same situation, here are some of things I have discovered.
There are tons of other good food, but you have to discover for yourself or ask around what locals eat.
Payments and vocabulary:
Some place you can pay by Suica or Pasmo card (the same card you use for the train!). If you buy a bento (lunch box), the cashier might ask you: atatamemasuka ? (Do you want to warm up?) They might also ask: ohashi ? (chopsticks?) If you don't need it, you can say daijoubu desu (I am ok) and if you do need it you can reply: onegaishimasu (please). Also in case you don't need a plastic bag, you can say fukuro irimasen. Sometimes they ask you also if you have a point card. You can answer arimasen if you don't have one.
Please note that I am not a native speaker and other ways to answer are also possible.
Differences between Konbinis:
The main companies are 7Eleven, Family Mart, Sunkus and Lawson. Prices and products vary between eachother, but most open 24/7 and have bathrooms and sell alcohol. I think the main distinction is that 7Eleven's ATM take international debit and credit cards.
For the rest is probably a matter of preferences.
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