Someone else mentioned it, but it bears repeating.....
How old is your car, and what are you comfortable doing on the side of the road? And I'll even add in, do you plan on being able to help others in need?
I keep a pretty good tool kit in my truck, but being as it's a 2016, there's only so much I can do without a diagnostic tool and a trained tech. The tool kit is more for rescuing others, or if there is an issue with the camper when I'm towing.
I keep a medium sized tool bag, with basic hand tools, and have consolidated where I can:
- 3/8" drive with both metric and SAE in common "medium" sizes (12mm - 17mm and 1/2" - 3/4") The sockets all ride on the same rail to save space, and I keep a 3/8" to 1/4" reducer on there as well
- 1/4" sockets in the smaller common sizes (below 12mm and 1/2")
- Multi-bit screwdriver, and a bit set. Bit set has both Phillips and straight blades, large and small, as well as some various torx, and other bits. Sounds like a lot, but the whole set could fit in an Altoid tin. I also keep a 1/4" drive adaptor for the driver. This allows me to use the 1/4" sockets on either the driver (very handy) or the adaptor for the 3/8" ratchet.
- 1/2" collapsible breaker bar/ratchet - Don't remember where I found this, but it's got an extendable shaft, which is a great space saver. Fully extended its about 18", but collapsed it's only about 12". It's a cheapie, but strong enough to break lug nuts. I also keep a cheap set of double ended 1/2" impact sockets, that will fit most cars or trucks. Takes less space than a four-way, but gives me more sizes to work with.
- Large and small of each: adjustable crescent wrench, vice grips, and channel locks.
- Larrge, heavy duty screwdriver that doubles as a pry bar (though I do keep a small pry as well)
- Medium ball peen hammer
- Set of folding hex keys
- Folding razor knife and spare blades, as well as an old pocket folder
- Duct and electrical tape, small spool of electrical wire, small 'sample-size' can of WD-40, and other misc. stuff
- 25' of paracord (braided into about 18")
Sounds like a lot, and it probably is, but it all fits in a medium tool bag from HD. And remember, this is in my truck, and designed for worst case scenario. So I've also got tie downs, tow-ropes, fire extinguisher, first aid kit, and anything else I could need stashed in the cab.
But... you could easily pair this down to some basics to fit in the trunk of your cars. In the trunk of the wife's car:
- Small 14" tool bag. You can find them for as little as $6 or $7 dollars in WallyWorld, or one of the discount stores if you wanna go really cheap
- Stubby ratchet and adjustable wrench
- Small channel locks and pliers
- Small assortment of sockets (90% of her Bimmer is 8, 10, or 14mm, so I just have those and one or two others)
- Set of hex keys
- Bit driver with a few assorted Phillips, straight, and tore bits
- Duct/electrical tape, length of wire, paracord, and razor knife
Being a BMW, her car came with a small, decent tool kit, but it fits in the well where the spare would normally go (came with run-flats, so no spare tire) but you gotta lift up the rubber mat, carpet, and trunk 'floor' to get to it - not something you wanna do in the rain, at night, on the side of the road - so a bag just made more sense. It also came with a small 1st aid kit, which is nice.
80% of what's in my bags all came out of my garage, so I didn't have to lay out much $ at all. But anything you do need, you can buy at Home Depot or Harbor Freight. Just decide where you can cheap out, and where you can't. The Husky or Kobalt stuff from the box stores is good enough for tools that you may only use once or twice, but don't want total junk. The HF stuff is good for things you're just gonna abuse once, or you just can't f'up too bad, like zip ties, bunnies, or pry bars. Just feel the stuff in hand first, and decide for yourself.