I tend to head straight to the bathroom most of the time before I even get a cart. I also try to go to supermarkets with clean bathrooms only. It is funny. I never worry about if I will make it to the bathroom or if in that moment are the rooms clean. My worries are...will somone take my shopping cart away?
One thing you can try if you are flaring really bad is to have home delivery of your groceries. My wife and I do this on occasion. We use Fresh Direct or sometimes a local place that delivers to our area.