LAX: A classic... a run to In n Out!!!

And before anyone asks and then someone else responds with a "SEARCH," just take, what was it, the Parking Spot Shuttle to Sepulveda and walk the rest of the way? On the way back, you'll probably have to "tip" the driver.

Also, if you go to TBIT and sit in the Daily Grill, you can leech free wifi from some of the clubs (I used CX's).

SNA: Go gawk at the statue of John Wayne, in between Terminals A and B. Then step out onto MacArthur Blvd... there are a few restaurants out there, including Gullivers (steakhouse) and El Torito (Mexican + "Cantina").

SAN: Take a walk along that road in front of the airport, heading towards Downtown. Great view of sea vessels, especially the US Navy carriers FYI - for taking off/landing, most of the time seats on the left side (ABC) are the best view of the harbor, coast, and Downtown SD. Bonus: see if you can spot the submarine base.