Driving LA to SF
Not worth it. There is too much good stuff on both ends and very little in the middle. Stop off at a nice deli in LA and pick up some good sandwiches and drinks. Instead of a fast food place along I-5, stop at a rest stop and have a picnic. About the same price and time and much better and more relaxing. Even grabbing some bread, cheese, and fruit is better. There is a lot more on 99.
It would help to know what food you would really prefer.
Are you going to SF via Gilroy or Livermore?
Here's a recent topic to explore:
Some posts have come up with Avenal recently:
The midway point is a toughie...Debbies Place in Avenal or Harris Ranch.
Earlier, Titas or Willow Ranch at Buttonwillow.
If you Search on "I-5" or "Hwy 99" you will get some more recos.
If you want to be adventurous, use the Search Nearby function in Google Maps and browse through Restaurants. In addition to Avenal, Huron and Coalinga have possibilities. Take a chance and report back.
Find a good sandwich-to-go place near home or the freeway before you get too far out of town. Stock up and drive.
Hwy 99 really doesn't take much longer and has infinitely more options.