Keep an extra set of keys in your wallet -- one for the house and one for the car. Fasten them together with twisters from bread loaves, and they will lie nice and flat. (ADHD adults should just be sure to keep track of their wallets.)
Put everything that needs to go out of the house in one place. Then, take the items to the car as you head out the door, even if you aren’t going anywhere, so you don't forget to do so later.
Next: Getting Things Done