If my family were going on a road trip tomorrow we'd have...
A cooler with waters, a few seltzers, and a few sodas (you can stop for coffee and special drinks but it's also nice to have what you like at the ready and to have a few to put in a hotel fridge).
For DH: pecan snickers
For DS: bbq chips and tiny m&ms and sour strips
For me: nerds gummy clusters
I bring some fruit for everyone to supplement road meals: this time of year I'd have clementines, blueberries, grapes. Usually these go in the cooler in packaging that can be eaten and thrown away (I'm weird about rifling thorugh containers of moist fruits then keeping them around, so I'd have lots of small bags of blueberries as opposed to a single container).
We'd end up buying additional candy because we always do, redbull for DH, protein shakes for DS, coffee for me, maybe string cheese for me, and probably also more regional or interesting flavors of chips. Pepperoni rolls for DH if in West Virginia.