Saving money hacks/tips as a student

As an international student in Tokyo, I was wondering if there are any tips or advantages for students to save on money on rent ,restaurants, everyday items, Etc. My friends in Europe, enjoy some advantages and I hope it is the same here. If you have any tips , advice, places, websites, mobile applications, or anything else, please share it and I hope everyone will benefit.

Also, I would appreciate it If someone can explain the benefits of PayPay and Rakuten and how to use them smartly (I tried but I couldn't understand) Thanks!