For short drives, I don't take anything other than my wallet. Remember, I'm in NJ...there's something like 100 places per miles where I could stop and get help (even the area of our "remote" lake cottage has about 5 places per miles).
For longer drives, I bring a pre-filled gym bag that is always sitting in my garage. It contains a coat hanger (wire), leather gloves, needle-nose vise grips, can of fix-a-flat, duct tape (invented in NJ!), fan belt, some electrical wire, a small tin can with various nuts /bolts/etc (a "he11 box"), some common "inch size" wrenches and sockets (cheap import stuff) and a few screwdrivers....and a cell phone. If, by chance, I feel a spare tire is needed, I have to carry it inside the car (due to fuel cell consuming part of trunk space). I hate to say this, but occasionally I've used some of the "road trash" along the side of the road to help with repairs (i.e.-jugs for carrying water or bits of wire to "fix" things).
While I agree that good maintenance will prevent most problems, there also seems to be some sort of mystical, opposite correlary. If you bring along a certain spare part, *that* part never fails. (i.e. -I've never had a distributor fail while carrying a spare one). Sort of a "reverse-Murphy's Law".....works on Italian and French cars too!
My girls taught me something interesting: Never sign up for AAA until you need it ("AAA" is a roadside emergency service used in the U.S....most folks use it a towing insurance, although it has other benefits). When the key sheared in the Sprite cam-drive sprocket a few years ago, I took out the AAA phone number, called them, and signed up (using my credit card)....then I hung up and called them back and asked for a tow truck.....they don't seem to care. And I never renue my AAA....I just wait untill I need it (my cousin is a VP for AAA.....he says they still make money on this).
For really, really long drives I do this:
https://www.britishcarforum.com/pictures/sprite_512.jpg