20 brands in the same 1-2 state US trip. Say, driving from LA to Vegas. Places like KFC, Arby's, Burger King, Wendy's, Taco Bell, Subway, McDonalds, Dunkin Donuts, Carl's Jr, Dairy Queen, Chick fil-A, Del Taco, Jack in the Box, El Pollo Loco, Panda Express, Red Lobster, Chipotle, Chili's, IHOP, Hooters, Olive Garden, etc. Most of these are just going by roadside signs. There are loads more that you generally get within cities (Five Guys, etc).
Wikipedia has this list, which shows a lot of variation, but I'm not sure how reliable it is with smaller chains. https://en.wikipedia.org/wiki/List_of_fast_food_restaurant_c...
Also depends on where you visit: the largest cities often have a lot more brands than more average places.
Frequency and traditions of eating out/cooking at home very likely play a role, as do food preferences (does a bakery chain count?).