If you are going to be driving for 8 hours I would be much more concerned about legs getting cramped up. I would rather say, stop several times, walk when you stop to get something to eat AND drink plenty of water... this would mean also stopping for restroom breaks. Almost nothing worst that getting yourself dehydrated the day before a race.
If you still feel you'll need 'snacks' then I vote for stuff that's easy to eat, not too sloppy...hopefully you're not going to be digging through a cooler and driving at the same time...
I drove eight hours last year the day before Myrtle Beach (and then they cancelled it) and stopped three times, once for an early lunch, one rest stop and once for gasoline. I think the walking I did and the water I drank was more important than what I ate.
What do you usually eat on the day before a race? for me it's "nothing spicy" and not too much.
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