Jump-start your car
Look, it's not that difficult. Positive clamp on dead battery. Positive clamp on good battery. Negative clamp on good battery. Negative clamp on bare, grounded metal on car with dead battery. Start good car, wait a couple of minutes, start dead car. Unclamp everything in reverse order and do not touch the clamps to each other. Now go drive your car for a while to let the alternator charge it up.
Or, you know, wait a few hours for AAA to send someone.
Change a spark plug
Unless your car is 100% electric (Nissan LEAF, Tesla, etc.), you've got spark plugs. While they certainly will last an order of magnitude longer than plugs in the olden days, they still need to be changed, and dealerships are truly thrilled at the prospect of overcharging you to do something that can be done at home. If you don't know what you're doing -- and it is a bit more involved than it used to be -- head to YouTube and you'll almost definitely find someone changing the plugs on a car just like yours.
Change a radiator hose
Some cars today have approximately 947 hoses, and you'll never get to all of them if you're attempting a DIY repair on the side of the highway. A coolant hose, however -- the big hose that runs from your radiator -- is the one most likely to go, but it's also the easiest to change, usually.
Identify and change a fuse
Chasing electrical problems is the bane of every shade-tree mechanic's existence. For a given problem -- as in, your taillights all went out at once -- you should first hope that it's just a fuse, then proceed to track down the appropriate culprit based on the symptoms. See your manual for a fuse map.