Good places to eat close to I-40
Just guessing, but aren't you only going to take I-40 as far east as Nashville and then go south on I-24 down to Chattanooga (and thence to Georgia)?
We drive the Nashville to Memphis leg fairly often and plan stops in Memphis or Nashville; aside from Jackson, it's a pretty drive but we haven't found a good stop.
A fall back location is always Cracker Barrel with a broad selection of to-go meals. Dependable and fast.
Hopefully, some good suggestions will emerge from your asking.
Shallots is right, unless there's something I'm not aware of, the stretch from Memphis to Nashville is pretty stark as far as good places to eat.
In Memphis, you can get off I-40 at Exit 1B shortly after you cross the MS River. Go North on Danny Thomas and turn east/right on North Parkway. Cozy Corner BBQ is on the right. Very close to the highway and great ribs.
Downtown Memphis, right after you cross the river, is full of great restaurants. Rendevous, Gus' fried chicken, Little Tea Shop and plenty of upscale dining, such as Felecia Suzanne, Flight, and McEwan's. If you take 240 south around town (40 doesn't go straight through), get off on Poplar and you are within easy striking distance of Hog and Hominy/Andrew Michael, Southward and Owen Brennan's (great for lunch).
Like everyone says, there's not much. However, if you are a fan of a great fried baloney sandwich, you can pull off I40 at the Bucksnort exit and stop at the little gas station/market/diner-type place, where they will fix you a good one and tell you about the escaped convicts who almost got away, but couldn't pass up the chance to grab one last sandwich. They got caught as a result, but apparently said it was worth it. It's not the best I've ever had (that's at Payne's), but it was good.
You might not find anything right off the exit ramp, but going by Helen's in Brownsville for BBQ would make your entire trip worthwhile. It is worth every second of extra time just to meet Ms Helen and her husband too if he is there! Another option that isn't to far off the beaten path is the *original* Gus's Fried Chicken in Mason, TN and Bozo's BBQ also in Mason, where I had lunch just yesterday. You won't go wrong with any of these, read the reviews on Yelp!