J.B.
portable dvd player-
gum or a bottle for take-off and landing
any sort of game thingy
cheap little toys picked up a dollar store- bring them out 1 by 1 as they get bored of the previous toy
drawing pad and crayons
you can "try" benadryl- call your doc for dosing- and try it a few days beforehand- I couldn't use it with my daughter because it made her hyper.
try to schedule your flight around nap, or so early he's likely to pass back out once he relaxes.
for the youngest- lots of stories and maybe a little tv time with airplane and boat themes. talk postively about how much fun it will be and how magical these things are- you can help built their concept of what to expect.
as the day for flying comes up- talk to them about what will be happening and what to expect. more often than not kids respond poorly to situations because they do not know what to expect.
As for the daycare thing- take him to it. Let him explore it with you there with him (security for him). Take him out- go eat breakfast or whatever.. Take him back- do it again- AGAIN explain to him "daycare is a fun place for little kids, like you. There are lots of other little kids here playing, do you want to play with them??" keep building that rapport till you're able to leave him there without him flipping out. The idea is allowing him to build trust in the new situation through his security in you.
I strongly advise against given sugary sweet "treats" on a plane. Hyper kids that lose patience or become bored are amplified with sugar.
Best wishes!