Power first. A decent 12V charger that actually pushes fast charge & one USB-C and one Lightning cable and each labeled and secured with a small velcro tie. If your head unit is old, an AUX adapter or a tiny Bluetooth dongle stops the family podcast war. I keep the cables and a flat power bank in a zip pouch in the console so nobody walks off with them. Spare wired earbuds live there too for the kid who forgot theirs.
For actual problems, the minimum that works is a jump pack, a compact inflator, and a tire plug kit. Add a headlamp, nitrile gloves, a microfiber towel, and a roll of tape. Two granola bars and a bottle of water get rotated monthly. A tiny first aid pouch with bandages and ibuprofen handles the rest. It all fits in a shoebox-sized bin in the trunk.
