Griot’s Garage sells a compact roundish bag that holds 6 8-ounce bottles to hold such products as Spray On Car Wash, Speed Shine, Window Cleaner, Interior cleaner, etc and space for a handful of microfiber towels. I also add in a Freezer gallon size bag for additional mf towels that fits inside.

I pack at least 1 Qt of oil and a funnel, a folding cross lug-nut wrench, and a bag of car emergency items including a compact battery with enough juice for a jump start, a blanket, jumper cables, a flashlight.

I also carry a compact tire inflator and tire plug repair kit. A tool book of essential sockets, wrenches, drivers.

All of this fits into the trunk along with two carry-on size suitcases when there are two of us.

I have a type of garment bag that holds more shirts on hangers, if needed, that hangs off of the headrest behind the seat(s), and I have a removable trunk mounted luggage rack for larger items if needed. We used it to carry beach chairs to Homecoming III.