I use a DryFob for the truck key and fob.
I wear a sealable waterproof pouch on a lanyard around my neck with driver's license, some cash, things I'd rather keep dry but won't be destroyed if they get wet.
Sometimes big advances in quality of life come from simple innovations in practice. I use towels to protect the seat. After repeatedly struggling to get a large towel to cover the back and hang down and cover the seat, I started using 2 towels. Much easier and worked much better.
I don't use a gear bag or regulator bag for shore dives. Once you put a tank on your BCD, it'll be pretty stable and not roll. You can use that, and/or the loose BCD and fins, to prevent tanks rolling across your regulator, consoles, etc...
Dive boots do fine for going in stores; no need for flip flops, though if you want a cheap pair, that's cool, too. There is something to be said for letting your feet dry out a little between dives. You can also shop in your wetsuit if you want.
This last trip I didn't find sunglasses as essential as I might've before. In the past, I tended to buy roughly $20 'Sunshield' sunglasses from Walmart; big things intended to fit over your regular glasses. A friend called them my 'birth control glasses.' Nobody has ever yet stolen a pair from me.
I've used maps from widely available free pamphlet things in the past. You can print some maps at home and laminate if you want. As others mentioned, cheap stuff you could live without if it walked off may be okay to take.
I use spit for defog; I never run out or forget to bring it.
I stow a scuba tool somewhere in the truck (maybe $20?), an o-ring kit, a little adapter that can be put on a low pressure inflator so it can air up a flat tire, a book on Bonaire dive sites (the Reef Smart one - highly recommended), a map, some plastic soda bottles refilled with water, various things in the truck.