I've stopped carrying co2 in favor of a mini-pump. some sealant mfg's state that co2 will cause the sealant to not perform properly. I'm not sure what that means exactly, but I would guess that it somehow causes the sealant to set or ball up. also if you are fighting a leaky tire a mini pump will not run out of pressure.

I also purchased a dynaplug kit which has allowed me to plug a couple large holes that sealant alone would never have taken care of, therefore not having to dismount tire and install tube on the side of the road. all you do is insert plug into the hole, let the sealant do its thing, and top off psi. well worth the money.