another good thing is a dum dum lollipop for takeoff. They are small and easy to carry and deal with and he will be sitting with you anyway so you can watch for choking . Plus they are sweet and they will lick them and swallow even if being stubborn and not wanting to drink, and best of all no spilling!
My kids flew thousands of miles as lap babies. another thing is when they come thru with drinks get a plain cup of ice and another empty cup. Mine spent a loooong time just playing with the ice. taking it out of 1 cup and putting it into the other or on the tray and back and forth. If it spills or melts no harm done to person, clothes or seat, it is just clear water.