We just covered this turf a week ago, when called to assist one of my sons with his moving back to Louisville from Phoenix. The El Reno (OK City) to Gallup stretch is one long day for us. Amarillo,TX is the main stop of the day one that leg of the trip. Beans and Things on Amarillo Blvd. (1700East) is reviewed in Stern's book, and I recommend it for a "buy it and take it with you" BBQ stop. If you are ready for a sit down BBQ dinner/Lunch try DYER's (at exit 68B off I-40) Order by the plate or the AYCE. The sausage isn't one to jump for and they use Pork Loin instead of Shoulder...It is good, but came as a suprise to us Pig-Pickers. The Brisket is Good and so are the Ribs. We didn't try the Ham.
Another stop for snack stuff is at Jiggs Smoke House on the west side of Clinton,OK. Jerky to go, and finely choped BBQ are available. The jerky can keep kids gnawing peacefully for miles !!
I second the Santa Rosa note above...There are a couple of Rt 66 places along the old road in town. Take a run thru the town if it is break time and enjoy an old time experience.
BTW Gas Prices are lower in Amarillo than the rest of Western TX and eastern NMex. Tank up there! Last week we paid 1.35 there, and saw nothing but 1.49 to Albuquerque...where it dropped to 1.35 again...go figure.