Grab a taxi and go to In-n-Out Burger (its right at the end of the runway - you'll probably see it on your descent). Have taxi drive through the drive-through. Order a double-double with onions, fries and beverage of choice. Offer to buy your cabbie lunch as well. Take taxi back to LAX and sit outside and enjoy your lunch in the beautiful SoCal sunshine. This will run you about $20 for the taxi and about $5 for the burger ($10 if you buy the cabbie lunch too).

This is what I do on my layovers through LAX.