Another vote for the electric cooler. Coleman makes a nice one. We've borrowed my parent's electric cooler for a few trips now and plan to just buy our own - it's so handy. It has a 12v plug, so you can plug it in to the car outlet while traveling, and then it has an adapter so you can plug it into a regular plug at the campground.
We have a fridge in the popup as well, but found that this is a great addition to hold all our drinks and we keep it outside the camper under the awning. That way, the kids aren't running in and out of the camper all the time to get a drink.