Club planes are simple. Combination locks on the hangar doors. Keys typically hanging from the Kollsman knob on the altimeter (or sitting on the glare shield). I've never been locked out. Now, could I forget the card key to get through the fence? I could, but it's in my flight bag with all the other crap I take with me when I go flying. The worst inconvenience would be to leave it in the pocket of the flight bag before leaving home. Then I'd have to get out of the car to retrieve it to open the gate at the airport.
Maybe I just haven't been flying enough to have forgotten it yet. I need to get my back fixed so I can regain my medical and go fly. July 20 last year was too long ago.