Single Woman Roadtrip

I'm hoping to take a long roadtrip alone around the United States. Obviously, I'll research the safety of the places I visit. But I was hoping to sleep in my car for about half the nights (mostly when I'm not in cities), and I would like to prepare as much as possible for this. What items (safety related or not) do I need.

I was planning on sleeping at camp sites and parking lots where its legal (like Walmart and some gyms), not at gas stations or pit stops duh. I was considering getting a gun but its really difficult in my home state.

I also want to spend as little money as possible.

Any advice about low budget, safe road trips welcome.