Flying is not fun but with the right preparation the experience can be enjoyable. It's all in the attitude - follow the ideas below to make your long flight day a pleasant experience.
Pack for the flight, not just the destination. Bring a decent sized carry-on for snacks, toys and other flight essentials. Games on your cell phone or other mobile devices can be great entertainment. You can use them through most of the flight if there is no wireless signal emanating from them. Bring your own ear bugs or headphones so you can watch the movie and listen to music.
Dress for comfort. Wear loose clothing. Flying is constricting enough without adding to your own discomfort. Wear light clothes and bring a long sleeve shirt or sweater. You never know if your flight will feel like a 100 degrees or 40 degrees. The settings seem random so prepare for any temperature. Consider wearing slip-on shoes. Not only will the security line be easier but it's easier to sit for long periods if you can kick off your shoes and wiggle your toes.
Start out the day with stress avoidance. Get to the airport early. If you think you need an hour and a half, get there two hours early. Don't try to barely make it; it's not worth the stress and the hassle if you miss the flight. Once you get through security you will likely have an hour or more before your flight.
Find a restaurant with table service for a relaxing breakfast. It's easier to be waited on than try to balance a tray while pulling your luggage and carry-ons. Most airports have at least one nice restaurant where you can relax with the newspaper or watch planes take off.
After you finish your meal, stop by a shop for flight essentials. You will need a bottle of water at minimum. Don't fret on your flight because you're thirsty and the beverage cart is nowhere in sight. Be in control of meeting your own needs. Use the beverage cart for bonus drinks of juice or your favorite drink.
Buy items to keep you entertained unless you packed them from home. You will need a good book (a fun bestseller not a "good for you" book), some snacks (assume the airline won't give you anything and you won't be disappointed), ear plugs to tune out the crying babies and chatty neighbors. You may want a crossword or Sudoku book as well for more diversion. Don't forget the pencil.
Once you are in your seat, relax. Read a little, nap a little, and watch the movie. If you keep yourself entertained the flight will pass quickly.