From painful experience, if the puncture is not too large, the Fix-a-flat will seal it .(you have to follow the instructions and get the bike rolling as soon as you can after putting to goop into the tire.  This spreads it all around inside the tube and is what produces the seal.)  The problem is that the aerosol in the can will only bring a rear tire (They are the ones that always seem to go flat.) up to about 10-15 pounds of pressure.  After riding slowly for a mile or so, the CO2 cartridges are to bring the tire back up to 30-35 psi.

The toilet paper is for the obvious.  It is also handy for wiping oil and fluids and such up after making roadside repairs.