Lung Wah Chong Chinese Supermarket
The major supermarkets can get one down: empty shelves, dented cans and wilted unidentifiable green things. It doesn't have to be this way. Most of the products of LWCHS come all the way from China, Thailand, and Japan but they seem to make it more reliably and in better condition than those from the Sainsburys distribution centre.
The store stocks goods that might otherwise involve a trip to London: tofu, miso, sweet chilli sauce, Thai fish sauce, soy sauces, noodles, more noodles, spices, MSG (by the bagful), some vegetables and frozen chicken feet... Worth a trip for anyone interested in East Asian cooking and cuisine.
Perhaps not the cheapest but it's hard to find comparable goods elsewhere in Oxford.