A normal supermarket. There are products, semi-finished products, and ready-made food. I have not seen analogues in Thailand. Yes, in private shops, probably, products can be bought cheaper. But if you need a choice, then there are no other options.
The best store for Russians in Thailand is full of them, they are small, but there is almost everything you need there. Even ready-made food. Salads already cut with dressing, rice with meat, burgers, yoghurts. Everyone will find food to their taste. There is beer and soft drinks. Honey is very tasty here, try it