When travelling, I put all my stuff in Rubbermaid Roughneck containers as well as the cooler, water, suitcase, chairs and rain shelter in the trailer. Those containers are stackable, rugged and come in different sizes. I'm partial to the 53L/14US gallon sized ones. Here in Canada, they are around $8.00, but I'm sure that they are cheaper in the US.
While camping, non-food items can be left outside and stay dry. Food and unwashed dishes go in the car. I have yet to pull a Walmart parking lot all nighter, but if I did, the boxes could go in the car.
http://www.rubbermaid.com/rubbermaid/pr ... rod2936118
It's amazing how much crap you can carry. A former friend of mine and I used to tent camp in a Chrysler Daytona with all gear and two dogs. Crap was falling on us, but we managed to go far. From Ottawa ON, we went twice to Florida, once to North Carolina, once to Nova Scotia, and another time to Maine. With my trailer, even my itty bitty Aveo can drag lots of stuff, which is good, because I seem to enjoy solo camping more.