@JLeslie You are right to a point. Petroleum jelly will seal off the mucous membranes from germs and viruses, but in the process will also store them live and in concentration. Blowing or rinsing out the nasal passage later will release them—into your mucous membranes. You need an ointment that will kill the germs upon contact.
As to hydration: you begin hydration hours before the flight, not during. It takes your body time to disperse the liquid where it does the most good; in the muscles (including the heart muscle) and between the layers of fat under the skin (storage for continuous use). Water is the absolute best hydration liquid. Many sodas, especially those with caffiene, tea and coffee work as diuretics, so your net hydration with these is often zero or less. Sugars thicken the blood. Alchohol dehydrates.
During sterile procedures we were required to wear paper surgical masks. We were also required to change them every fifteen minutes because that is about the time they become ineffective for filtering out germs. Once the mask reaches a certain level of saturation from the atomized moisture of your breath, they no longer work. This was common surgical protocol put into place by the recommendation of the manufacturers and the FDA.
Im with @Apparently_Im_The_Grumpy_One on this. I stopped travelling with carry-on bags years ago. Before 911, I sometimes carried a comb, small folding toothbrush, and a small tube of toothpaste in my pocket on long flights. After 911, I travel with nothing. Anything I need, I buy at the other end, including one change of clothes if they lose my checked baggage. When traveling, cash is king, easy to carry and easy to keep track of.