I agree with the previous poster... relax! it will be what it will be... granted, 16 mos is a difficult age, but you'll survive. I've mostly found pretty kind hearted people on flights who remember being in your shoes... so try not to worry too much. plus the flight attendants have seen it all, and are usually pretty helpful.
try to get a seat in the bulk head... there will be a little more room so he can at least stand up or sit on the floor (bring a blanket). bring a variety of his favorite snacks... (just be sure it is stuff easy on the tummy... kids can get a little barfy on planes. bring a change of clothes for him (as well as a shirt for you and your husband... my daughter barfed on my husband last christmas... fun stuff).
toys that are new to him are great... will he watch a dvd? those portable dvd players aren't terribly expensive (or make it an early xmas present) and might buy you a few minutes of peace. be prepared to sing his favorite songs... maybe teach him some finger games (where is thumbkin, church & steeple, etc.)... gate check your stroller (best thing to have when you get off the plane at your destination).
relax, breathe.. good luck!