When parking on a hill, apply emergency brake before shifting to park. This puts the force that prevents the car from rolling down the hill on the brake and not the transmission.
Recent Optima batteries are made in Mexico, not U.S., and quality dropped (while price increased). Avoid Optima batteries.
AC Pro Super Seal recommended by Scotty for small AC leaks.
Ethanol is common additive, but should not be more than 10% or can damage the engine. You can buy a device to measure ethanol content.
When jump starting car, let the running good car charge the dead car for 10 minutes, then turn OFF the running car, then try to start the dead car. Don't keep the good car running while you try to start the dead car--that could mess up computers, etc.
USB adapters for your car are more complicated than they look, and cheap ones can cause unexpected problems.
Check your car model for recalls.
Boslla LED Headlight Bulbs are spendy but look very effective and adjust to visibility conditions. Very cool. https://amzn.to/2UQTjAZ
Silicon lubricant for window rubber and Nu Finish polish in place of RainX for window for beading water.
Don't bring into the negotiation any trade-in car until you've finished negotiating on price. Arrange any necessary auto loans ahead of time with your bank or another reputable credit source--DON'T USE DEALERSHIP for financing.
Replace the radio in your car w/ android.