That depends quite a lot on what you like to listen to...

Mine's got a little over 7 gb, and I'd guess probably a solid 6.5 of that is country.

Just out of curiousity, why don't you put songs you have on CD on there, though? I find that even if I have the CD in the truck, it's easier to play it off the iPod than to root around for the CD case, then find the disc, and put the one that's in the player back into the case.