I can't comment on Buc-ee's personally, but my friend in Dallas swears by them. She specifically mentions Beaver Nuggets all the time, which I guess is like a cross between caramel corn and Cheetos. Their BBQ is on my list of things to check out when we fly down for our cruise.
As for Rudy's, I've never bought gas there, and the one in Colorado sort of seems like the gas station was sort of an afterthought, but I highly recommend it. In fact, it is probably my favorite BBQ place in all of Colorado. I live about 3 1/2 hours away from it, and I make a point to stop at Rudy's every time I'm in the area. Their moist brisket is a bit pricy if you ask me, but well worth it. I'll be trying Buc-ee's since we have Rudy's close to here, but if you want to give Rudy's a try, you won't be disappointed. (Well, unless you are a vegan or something)