I prefer a frame pump to the CO2 cartridges, but then I'm pretty retro in that regard. I also see far too many used cartridges littering the side of the roads where I rode.
At a very minimum, I recommend a tube, and full patch kit. If you're OK with a little more rotational weight, I put Mr. Tuffy tire liners between my tubes and tires and filled the tubes with slime, and that helped a lot with all the puncture vine in CO. An extra small seat bag should hold a tube, tire levers, patch kit, and possibly a multi-tool (I highly recommend one with a bag to keep from ruining the tube). Again (my personal choice), a frame pump under the top tube, and you'll be set for most anything. For long tours, get a couple spokes of each size needed and tape them to your right chainstay (it'll help keep the chain from hitting the frame, and if you break a spoke, you'll have the right replacement handy).
Good luck with whichever choice you make!
Vol