I've flown by myself, three times with Lil on my lap and my wife and I are flying again with her next month when she'll be 9 months old. It's a challenge, but anytime you travel with kids, it's a challenge.
I second the idea to bring new toys as well as a couple old favorites. Feeding finger foods (puffs, cheerios) will help pass the time. Lil likes to stand on my lap, so I'm sure that's going to happen. Last time, I spent much of the four hour plane ride, walking up and down the aisle. She was happiest when I was in motion and I think she just liked checking out the other pax. I got my exercise on that trip!
Diaper changes are a challenge. Ask the flight attendant which bathroom has the diaper changing station in it. Not all bathrooms do. Bring a big bag packed with diapers/wipes etc and if you have to change a diaper on the plane, just bring one diaper and a handful of wipes in a small plastic bag with you to the bathroom. There's no room for the big bag and the plastic bag can be zipped shut before disposing of the dirty diaper in the trash. Other pax will thank you for that.
I also wore Lillian in a Moby Wrap and now that she's too big for that wrap, I'm planning on wearing her in a Mei Tai to get to the plane and bringing the Ergo for the parks.
For saftey in flight, I put her in the Baby B'air Flight Vest
http://www.babybair.com/ that basically buckles her into my seat belt and keeps her safe if there is turbulence.
The best advice my mom gave me, don't worry about what other people are thinking. We've all been on flights where there's a screaming, unhappy baby and glaring at the parents, or sighing in frustration, certainly doesn't help the situation. My mom reminded me to keep things in perspective. Our time with the other pax is a short period of time in their lives. If Lil is crabby, it may not be a pleasant time for those around, but they'll get through it and then have a story to tell when they get off of the plane.
Try not to stress, because the kids will feel that stress and be more likely to act up. If you are chill, there's a better chance that they will be chill. Good luck!