HI lucky duck
We've been back about 6 weeks now. We go every year and love it. I don't know of any large supermarkets in Patong but, there are smaller supermarkets. The one underneath Ocean Plaza is where we usually buy our beer to have in the room. Ocean Plaza is right up the other end of the beach rd from the Novotel. As far as spirits and wine go, we usually buy from Duty Free and take with us. My partner also buys the Thai whiskey over there, which he sometimes picks up quite cheap. Thats not for me though. That covers our room and balcony. After that there are some great bars along the beach rd.
Have a fantastic time.