I have done 5 flights with my 12 month old and it's only the first one that is daunting!
For formula, take a couple of clean bottles. Measure the formula into a divided container - Avent do one - or into individual plastic food bags. That way you know that each makes XXml. As you need to feed baby, ask a flight attendant to fill the bottle to the required volume with room temperature water, add the powder and shake. If your baby likes the milk warmer or cooler, adjust the temperature you ask for. They can also wash the bottle for you but can only sterilise with boiling water. It's not really an issue after 6months, but if you are bothered take lots of clean ones.
Take a few new toys/books and produce them one at a time at intervals throughout the flight. The emergency instruction leaflet is good for giving to the baby too as it is laminated. At a push, give the child the inflight magazine and let them trash it.
Keep a vomit bag available in your seat pocket. Use it as your trash bag and hand in to flight attendants at intervals requesting a new one.
Only take what you need with you in your travel bag. I don't take anything for myself anymore and use the space for my baby's stuff. If it has a wide top openning it is better as you can rummage around a lot.
Take a few muslin cloths too to put over the seat/yourself/baby as protection and to mop up spills etc. They are also good for improvising games.
Airlines supply nappies, so I don't even take them with me anymore and just ask for one as I am on my way to the loo with baby. Don't forget wipes - they are invaluable.
Make sure you order a child's meal a few days before. It's almost worth calling the airline reservations to check they have got this listed. Also be prepared that your child will want to eat whatever it is you are having (but that's OK, as kid's meals are more interesting than economy class meals). I also take food bags of Goldfish crackers or small none crumbly crackers like that. Grapes in a tupperware go down well too. In fact, snacks are the thing you should be sure to take in those resealable food bags, as airline peanuts and crackers are not ideal for kids. Make sure you get the child to drink lots too to keep them hydrated.
On my last flight I walked my baby up and down the aisle almost the whole flight as it was a day one. Noone objected and in fact it was hard getting people to stop touching her cute chubby cheeks! I also took her to the back of the plane where the loos are and we sat and played on the floor out of people's way.
One thing you really need to remember is not to let other people's potential frustration bother you. Unless your kid is really screaming, it doesn't actually carry far beyond a few rows. Very rare are the people who will be pissed off and will let you know so. Most people are sympathetic. I know I am quite stressed whilst on the plane but do my best not to let the baby know it. That way she isn't stressed either. It actually brings tears to my eyes when people say nice things to us, and just knowing someone else is willing to help can be a real calmer (so tell the person with the baby you will help them out if needed!!).
If your kid really starts howling, lock yourselves in the loo and play splashing game swith the water (dry it up afterwards)! This really gets rid of a tantrum and also allows the kid to let rip with minimal effect on other passengers. The loo is also a great place to discipline your kid if (for eg) he is kicking the chair in front incessantly. I don't mean take the kid there and beat them, but take them there for a quiet word in their ear.
Lonely Planet do a good book on travel with Kids.
[This message has been edited by BoardManager (edited 29-10-2002).]