I have an under the seat bag that I have a spare tube, 2 tire levers, co2 cartridge and inflation device, chain breaker, quick links, quick link tool, hex wrench tool (multiple sizes) phone, ID, credit card/cash, and car keys. I've only had to use the chain tools, never needed to switch the tube out. After I have to do that once I will determine if the co2 way is sufficient, or if I should get a small pump to strap to the tube.
BTW this is all for my 29er MTB