For the most part, people just take clothes, toiletries, and some snacks. They usually don’t take a ton of food because there are so many roadside restaurants and convenience stores that it’s usually easier to buy what you need than trying to transport a bunch of groceries. That said, if you’ve been on a road trip and dealt with issues (like having coolant pipes explode in the desert), you’ll bring a few tools and some basic vehicle supplies (oil, coolant) as well.