You’re in luck.
Warrenton has a Five Guys. They serve one of the best burgers in the U.S. http://www.fiveguys.com/
IMHO Willard’s BBQ is by far the best in the greater Metro D.C. area. They are just up the road in Chantilly and well worth the 10 mile trip from Warrenton. http://www.dcbbq.com/
Breakfast: on the way up 29 toward Chantilly you will see a "Country Restaurant" on your right about four miles North of Warrenton. Great stuff!!! Country fried steak and eggs! YUM!
If you have a fine dining yen, go West 211 about 15 minutes and find what has for 30 years been rated, often the very best, and always one of the five best restaurants in the United States of America. http://www.theinnatlittlewashington.com/restaurant.asp
Memories of the meals I enjoyed there actually raise the hair on my arms. Take your wallet.
If you have time for golf I highly recommend South Wales – go out 211 6 or so miles to the first light (Shell Station on your right). Turn left; one mile on your left. Extremely reasonable. Great layout by the same guy that desighed TPC Avenel.