In my opinion, you should consider buying traditional Japanese items like the Lucky Cat Maneki Neko, which is very popular. Also, Japanese chopsticks – they come in various colors within a set and are of great quality. They're not only stylish but also beneficial for health... and there are many more options available.
Yes, credit and debit cards are generally widely accepted in Japan, especially in urban areas, major cities, and popular tourist destinations. However, it's a good idea to carry some cash as well, as there might be smaller shops, markets, or rural areas where cash is preferred. Now, Japansese still use cash.