I would add that food appears to take an inordinate amount of time.
1) you can't just eat fast food (depending on where you go, you might not even find it!)
2) if you eat in non-fast-food restaurants, you've just sunk an hour or maybe an hour and a half. Per meal.
3) if you cook your own you'll be surprised at how much time you spend in grocery stores.
a) it's an unfamiliar layout
b) you may think you know what you want, but you don't know what they have to offer.
c) and you're doing it tomorrow (or the next day) again.
If you have very cheap and simple tastes (which I doubt or you wouldn't have posed the question), you can find the peanut butter, jelly and packaged bread in just about every store, and that'll meet your caloric needs, although not provide a whole lot of balance. It is certainly the fastest approach. Maybe healthier than fast-food. Depends.
I read a CGOAB journal in which the (tandem) couple appeared to be subsisting on bagels and spreads (peanut butter, jelly). They survived KS to NC, but they were ready for some different food after that.