Road trip with 5yo is a special kind of hell

"Are we there yet?" in various formats for 8 hours straight. Packed snacks, tablet, books, everything. Nothing worked for more than 20 minutes. By hour 5 I was considering just opening the door and letting him run alongside the car. Somehow made it but swore we're flying next time even though it's more expensive. Anyone have actual strategies that work or is this just the age?