Have spare keys made at a nearby hardware or home improvement store. Keep one key where you know you'll always be able to find it, and other keys with trusted family members and friends. You can always call one of them if you lock your keys in your car.
Consider hiding a copy of the spare key in a magnetic "Hide-a-Key" case. These are usually available wherever you have keys made. The case is used to hide a set of keys under the car by sticking the magnetic box onto any metal component. Choose a location that is difficult to see, but that you can easily remember.
Find out if your insurance company offers a lock-out service, where it keeps a copy of your key that can be delivered when needed.
Ask the police for help. Most police departments have tools, such as a "slim jim," that can reach the inner mechanics of the door to pop the lock. The best part of seeking help from the police is that the help is free and safe.