this seems rather reasonable to me.
breakfasts for me, I'm an oatmeal guy so thats inexpensive, even the prepackaged boxes, add some bread/jam or a muffin, some juice, some tea or coffee--Im sure a good solid breakfast comes out to $5
lunch-I tend to stop and buy bread, meat, cheese or whatever to make some good sandwiches. Fruit, tomatoes. probably comes to $10, with stuff left over for snacks
supper-pasta, some veggies, a can of tuna, or a can of spaghetti sauce, or some other meat to put in the sauce, something to drink, some sort of dessert--I figure its not out of line to say 10-15 bucks or so of groceries will get a good solid meal, again probably with leftover stuff for morning or another meal.
this is completely off the top of my head, but not out of the realm of reality.
Yep, Rowan and I eat a very similar diet to what you've described when we tour too.
Sometimes you can find stuff in the price range you've described there. Sometimes you can find good things on sale and can get away without spending too much. Other times you find yourself in a touristy or remote area, and everything is twice the price you had in mind.