Besides grocery shopping, on a long trip you will need to pick up various "other supplies" from home centers, hardware stores or auto parts stores. Try to be flexible in your arrival times because you can easily loose an hour or two with just one stop.
If you are like me, I always travel with a well stocked tool box and things to handle emergency repairs (stainless steel hose clamps, "bailing" wire, zip ties, hookup wire, heat shrink, duct tape, 5 minute epoxy, grease/lubricants, paper towel/rags)
Very long trips will likely require scheduled maintenance (oil change, etc).