I make no secret of the fact that we use Benedryl. Our daughter has really bad sinus problems and allergies anyway. Our pediatrician told us the Benedryl would help with the sinuses to relieve pressure pain on take off and landing. The one thing to keep in mind, though, is that some kids fall asleep with Benedryl, and it makes some kids hyper.
First time we flew, we did watch her reaction carefully when she got her doses in the days leading up to the flight to make sure she wouldn't wig out.
If the Benedryl isn't something you're comfortable with, take a pacifier. The sucking can help to relieve the pressure. (Our daughter wouldn't touch one with a 10 foot pole! Don't know why!)
We also took a DVD player and Baby Einstein DVDs. Those kept her occupied for quite a while.
Our daughter was also 11 months when we flew - so keeping her occupied was MUCH more difficult. At 3 months, I think once the pressure issues are resolved, all the noise and rocking of the plane would probably lull your little one to sleep.
Good luck!!!
