"These collapsible box/crate things. They lay flat in your trunk when you don’t need them, but if you need them to help keep groceries, fragile items, or whatever from rolling around your trunk, you pop them up accordingly. My dad gave me some and I’ve been using them for years, they’re incredibly useful."
#13 Tires don’t just go flat.
A couple of bottles of water.
A set of basic tools.