Our friend Google shows the closest In-N-Out at 9149 S Sepulveda Blvd, Los Angeles, CA, a scant 1.5 miles away.
There is also An In-N-Out in Kettleman City for the VanJam Contingent,
( a detailed list of the "Dining" options can be found here Interstate 5 California Southbound - Central CA - I-5 Exit Info) Although various sources have said that Harris Ranch has the best/cleanest "facilities" on I-5 Hiding in plain sight / I-5 icon Harris Ranch a haven for those craving anonymity -- and steak