I don`t really carry much in the way of tools these days, not all that much that either Accumulatorette or I will actually fix on any of the current vehicles. The Audis all have decent enough oe kits for the most part, the Crown Vic is as reliable as sunrise, and the Tahoe seldom goes too far from home. And yeah, a cell phone and AAA card can go a long ways, just be careful how others behave around your vehicle.
Every vehicle always has water, sanitizing wipes, a flashlight, an edged tool of some type, disposable gloves, a blanket, water, and some kind of 1st Aid kit (dog-haulers always have Quick-Clots and other dog-centric stuff). And always = ALWAYS, rentals included.
We do (always) carry both duck (no not the brandname, and not "duct") and electrical tape, a tire gauge, mini-jumper cables, flares/reflectors, and and a multi-tool in whatever vehicle we use for a real roadtrip, which have come in handy a few times (e.g., the S8`s Deer Incident).
We do keep an air compressor of the "just fills tires" variety in the Tahoe (under-vehicle spare = hassle). Changing tires isn`t that big a deal on the others, not like Accumulatorette needs help with a spare or anything...
And of course, we both carry the EDC/"don`t leave home without it" stuff, at least a flashlight and knife of some kind no matter what, every single time we go anywhere.