If you are driving through Oklahoma on I 40, heading west.
When you get to Oklahoma if you will take a slight detour from I40 you can visit our large health food store that has a great selection as well as a juice bar that has GF wraps and the staff is VERY knowledgeable in GF prep. You will be able to stock up on packaged foods. They carry a wide range of Glutino, AMY's, Kinnickinick- they have an entire GF section. It will be about an 8 mile detour but the highway wraps back around to I40.
Here is a map that shows the detour you will make:
Health Food Center
Their address is 7301 S. Pennsylvania Ave
Hours: 9-8 M-Sat, 12-6 Sunday. The juice bar opens about an hour after and closes 1-2 hours early.
When you get to MidWest City, Oklahoma take EXIT for I35 toward Dallas,
Then take 1240 towards Lawton
Exit Pennsylvania, it is located in a shopping center on the NW corner behind Hooters and Kinkos.
Then you will get back on I240 and take it to I44 where it will rejoin I40
You will be heading toward Amarillo- There will not be much between OKC and New Mexico.
Amarillo does have some restaurants like Outback, Carinos and Texas Road House which you can eat GF at. They also have a healthfood store somewhere there, we were there on Christmas day so it was closed. http://www.eat-rite.com/ - You might contact them and see what they have.
Then there will not be much until you get deep into New Mexico. So I would stock up in OKC. When I say not much- I REALLY mean not much- even the McDonalds are far and few. At one point we were stuck in ice and starving and the McDonalds Ceasar salad was as good as we could get.
Albuquerque may be the next chance to really stock up on feed. There are TONS of restaurants there.
Checkout http://www.roadsideamerica.com for the Rt66 attractions along the way. Cadillac Ranch in Amarillo is worth the visit. You can map out your route in the MAPS section and see what weird roadside attractions are along the way.