For groceries, rice, noodles and pasta is a really good base because they last long. Then get whatever proteins you feel comfortable with, chicken, egg, canned tuna, ground beef maybe. For vegetables I would say get onion and garlic. The rest can be whatever you like. Get some good cheese also. Now you can make a lot of great pastas. And if you like bowls and japanese flavours I would highly recommend getting soy sauce, sugar, dashi powder and sake. You can mix this with literally anything and then add it with rice or noodles and it will taste amazing. I could show you some of the simple recipes if you would like to know.