Hi RosieH,
Firstly this is a tour for fine scenery and not fine dining but that said you won't go hungry. Apart from Salt Lake City and Las Vegas you are not in big cities. RV's (camper vans in English) are everywhere and it is just regular people enjoying the scenery.
For myself I prefer to carry cash for my day to day spending and gave myself a budget of $50.00 per day. I did bring some back but can't say exactly how much as I cashed this in with some other currency.
Although I keep notes of my travels they do not include details of every meal!
however:-
1) breakfasts are included and are buffet style and you can have as much, or as little, as you want.
2) drivers need rest stops and you usually get stops mid morning and mid afternoon, unless these co-incide with tours/visits etc. Time for a comfort break and a drink.
3) lunches are variable. Sometimes at a place with a diner but often at a mall where there is a Walmart (a big supermarket if you are npot familiar with the USA) where you can get a salad or sandwich to go. I found this was usually enough after a breakfast.
4) dinner sort of depends on where you are but in Rapid City there was a Denny's across the road which serves meals at a reasonable price and elsewhere there was plenty of choice to suit all budgets. Americans dine out a lot so there are no shortage of eateries with plenty of choice as to what you might fancy for dinner.
I am not a big souvenir spender but tended to put that sort of thing on card leaving the cash for food and drink and day to day incidentals.
Ian