There is an In-n-Out right on Sepulveda north of the north runways. It is a great place for planespotting and is close enought to walk to (15 min), no real easy bus access, but a cab might be reasonable. Actually, it is located right next to the Parking Spot, I wonder if you might be able to hop on one of their buses (maybe give the guy a tip to let you slide if they require that you prove you are parked there).

I have walked there a couple of times, but it is along major roads with not large sidewalks, if you are leary of walking, the Parking Spot shuttle might be best if it will work.

Here is the link to the closest one link