We have spent 4 or 5 months a year in the MH for the past 3 yrs, and I can't say we shop any differently than we do at home. Now that we are going to begin full timing in June, I don't anticipate many changes in our food expenses.
I will still shop at Whole Foods, Wild Oats, and Trader Joe's (or similar organic, natural markets). Just because we are retiring, doesn't mean we want to cut back on the quality of the food we put into our bodies.

We have never eaten fast foods or processed foods, and don't intend to start now, when we need our good health more than ever.
We probably will eat out just as often, but cut back on the number of times we go to the more expensive restaurants.
I think most of us maintain the same lifestyle preferences when we go full time. We just live in an RV instead of a house... We can hardly wait...