Flight to Spain with a 3 year old-suggestions?

My wife and I are flying from Atlanta to Madrid in April with our 3 year-old son. He has only been on one flight before, and that was 2 years ago. I'm wondering what some of you guys have done to occupy your young child's time on a long flight.

Some people have suggested giving a little benadryl, while some do not think it's right. I personally don't have a problem with it, especially since many adults take things such as sleeping pills when flying. We will take his "computer" (a leap frog toy with games), some of his toys, and a portable dvd player with some of his movies.

We hope to keep him up the night before, and hopefully not allow him to take a nap (which many days he doesn't anyway) the day we are traveling. So, hopefully, he will sleep most of the flight. But, in case he doesn't, I want to have a game-plan. I think this will help everyone involved-us (the parents), others on the plane, and most importantly, our son.

Thanks!