I have lots of good experiences using Cold-Ease at the very first sign of a cold. You know, that yucky feeling in the back of your throat caused by your sinuses starting to drain. Suck on one or two lozenges and 9 times out of 10 the next morning you will have forgotten you might be coming down with a cold.
The magic ingredient is zinc. I have seen reports of independent scientific studies concluding that it really works. If you delay until you are sure you are coming down with a cold it will be too late. Taking Cold-Ease or some other product containing zinc will lessen the severity of the cold once you get it.
To prevent or alleviate ear blocks or sinus blocks due to swollen tissue once airborne, I second the recommendation for Afrin. The Navy flight quacks prescribed it. From personal experience, it works. Again, the sooner you use it the better.