I couldn't remember what I did about food. It doesn't get them wet or chilled if it spills so matters less if it is available all the time or just at the stops.
I looked it up
here. "We are on our third stop for food and water. It takes longer than fifteen minutes for them to be mostly done. They start peeping instead of twittering at about an hour. I think for food or water because the temp is about the same."
After reading the thread, I remember... the quart jar chick feeder clearly didn't fit in the box I chose because it was the biggest box I could find that would fit on the car seat. At least not and still have room for the chicks. Also, the feeder was heavy in general and top heavy with no easy way to secure from sliding or tipping over. Then it went well with food at the stops only.
I also had a thermometer, a method of keeping them warm, a method of leveling, cushioning, and securing the box, and a method of keeping them from jumping out of the box while still allowing good ventilation. And bought a better method of keeping them in the box after the first method failed halfway through the trip.