If I have room, I like to buy non perishable items before I get to any vacation spot. Not just the prices, but can't always find the things you need. Also, I don't want to spend any more of my vacation time than necessary shopping for groceries. I make a list of the perishable items that I need to buy once I get there, so I don't forget anything. I have on occasion even bought my perishables ahead of time, if it is not too long of a drive. Take a good ice chest and buy about $10 worth of dry ice. It will keep things cold for at least 8 hours and even keep some things frozen if you put it right on top of them. I think you will find much better prices in Corpus than Port A.