I think the best thing you can do to prevent getting a cold in the first place is eat right, take your vitamins, get plenty of rest.... In the past we've take Airborne right before our flight to help boost our immune systems. I also usually take sanitizing wipes and wipe down the arms and tray table on the airplane (I doubt they clean the planes that thoroughly). Try not to touch your face... wash your hands frequently. Sometimes if a colds gonna catch you, it just will so at least if you're pretty healthy to begin with, hopefully you'll get over it faster.
I've been seeing ads for Zycam, which is supposed to help decrease the amount of time you have a cold also, if you start taking it during the early stages.
hth.