My daily gets a tool roll from my motorcycle days (assortment of allen keys; multi-bit screwdriver - flat x2, phillips x2, torx x4 - some box end wrenches, small vise grips, small dikes, a roll of electrical tape and a bouquet of zip ties); small air compressor; rope tire plugs. No wheel lock key because I never use those stupid things. If they want your wheels...they're gonna get them. With or without the car. (When was the last time you heard about wheel theft? Seriously? Other than dealers losing 20 cars' worth in a night, that is...) My daily travels light as it's only a 2014 and doesn't leak or burn anything.
My work truck (2500 Cummins closing in on 300k miles)? Gallon of rotella. Gallon of coolant. Cargo straps. Tow straps. Tool roll. Some various hose clamps. Spare fuel filter. Multiple ball mounts (2" ball, 2-5/16" ball, varied drops). Keys to my trailers. Master keys for trailer cargo doors and door handles (used to work for an RV dealer). USB chargers for my tablets, phone, etc. LED flashlight (in addition to the one on my phone). And when I'm towing...a jack and a spare wheel for whatever trailer is hooked up.
In my motorcycle, I keep the same tool roll; the same compressor and plug kit; an LED strobe light; a quart of oil; spare socks (riding in rain is one thing; riding in rain with wet feet? SUCKS); spare gloves; one of the new cell-phone-size jump packs (need to get more, for the cars).
Toy cars? Depends where I'm going and how far away. I keep a spare tool roll in the garage and usually toss that in a 5 gal bucket along with fluids or cleaners or whatever the destination calls for (like, if I'm taking the Charger to a car show, it gets cleaners and rags). Cars that burn fluids? I carry a quart of each flavor, just in case.
On my person, always my Hellcat 9mm (licensed) full of Federal HST, and depending on destination, a spare 13rd mag or three. And bottled water. My truck is the "aging rock star" vehicle - tons of empties rolling around...but not beer bottles, Propel water bottles. Ah...age.
I preflight everything pretty well - comes from hundreds of thousands of miles on motorcycles (street, and track days), so I very rarely have a failure on the road. But, I do need to add a fire extinguisher to the lists...