For fixing roadside flats, your options are either a frame-mounted little pump or CO2 cartridges and an inflator head thingie. I prefer the frame-mounted pump. My experience with CO2 is very limited, but I don't like being limited to just a couple inflations. I do long rides (40-60 miles) in the country and multiple flats can happen, or one flat where you don't find the offending thorn or whatever and it gets you again. Plus CO2 cartridges- or at least the ones I've used- only get you up to 60-70 lbs of pressure.

Then in the fullness of time you'll want a floor pump with a pressure gauge.