For us it depends on where we are going, how far, what we plan on doing for the time we're there.
For long trips out of state we typically don't buy too many groceries until we get to our destination. On day of arrival we find a place to eat out and just relax.
On shorter trips in state we do most of shopping in advance. We like what we get from our local butcher. The fridge/freezer are just fine for the 3 or 4 hours most of our "local" trips take.
We have kept things in our fridge and freezer for up to 15 hours without having to run the propane. Just throw some freezer packs in both the fridge and freezer.