Since there's a 10000 character limit to posts I had to cut a bit out of the above post and felt that a few things that were cut are worth mentioning.
Airshows acts are generally arranged in such a way that the really big acts happen towards the end of the show. Plan accordingly. Nothing is more irritating than an excellent day of shooting only to discover you only have 3 shots left on your last memory card to shoot the Thunderbirds. There's two ways to avoid this. One, if it's your first show and you shoot RAW normally I recommend you try shooting in JPEG or it's equivalent. You lose some of the ability to easily fix some of your mistakes, but it'll increase the amount of shots you can take fourfold (at least on my camera it does). And two, shoot only the acts that interest you. This will be difficult to do, especially if it's your first show, but once you get a show or two under your belt, you'll have a better feel for what interests you and what doesn't. (Jet trucks don't do it for me, nor does Tora! Tora! Tora!)
Be prepared for disappointment. Missed timing, blurry shots, etc. Since you're shooting digital, shooting yourself happy isn't usually an issue, but don't go through the process of deleting all those less than perfect shots until
after you go home. You never know what you will miss happening in the air while you're deleting those bad shots.
Remember the static displays, they're easy to forget in all the excitement of the day. If I'm able to go to a show over multiple days, provided there is no change in the acts, I'll try to spend one shooting the flight displays and then another shooting the static aircraft and crowds. It's difficult to shoot both in a single day, so if you can break it up, more the better.
The best airshow is a free airshow... and there ain't no such thing as a free airshow. Oh sure, some have free admission, but $15 parking. Some have free parking, but $7 polish sausages and $4 bottles of water. Some just charge you tooth and nail from the get go. Bring plenty of cash, not just plastic. Many vendors at shows these days have the ability to accept plastic, but more can't than can. So make sure you have plenty of the green stuff (or whatever the color of your currency may be) for all the little things at the show. And be sure to save some of that cash for that souvenir t-shirt, poster, or patch.
A back up point and shoot isn't a bad idea if you have one. Of course this is more aimed at the DSLR folks, but you P&S types can benefit from this piece of advice too. The reason? For that buddy you brought with you. Bringing a friend, spouse, child, etc. is one of the best bits of kit you can bring with you and having a camera for them (if they don't already have one) is good so they can shoot a different perspective than you. And your buddy serves another purpose besides taking still more pictures, they can also run interference for you. By surrounding yourself with friends you thus create a force field keeping the little ones who are yammering for a better view from stomping all over you or your kit (it will happen).
Tripods, bad idea. Monopods, slightly better, but still a bad idea*. Either only gets in the way and makes things more difficult. A much better idea if you can afford one (it's on my wish list, along with a Bigma) is a
Bushhawk. I've seen these at shows before and panning with them is amazing.
Weather for airshows generally needs to be good, but sometimes it isn't. Make sure you bring any wet weather gear you have. Especially for your camera. A cheap rain coat or small umbrella can go a long way, and all those Ziploc bags you're hauling around really come in handy when the wet stuff starts falling. I bring mine regardless of the weather report because, gasp, weather forecasters have been know to get it wrong from time to time and there is only so much room for people underneath the wing of a Viper.
Shoot helos the same way you would propeller driven aircraft. The blades on a helo turn at a much slower rate comparatively speaking due to their size than a propeller, but getting rotor blur really makes the shot.
I'm sure there are more tips that I can think of, and I will continue adding to this thread as I think of them. I'm also happy to field any question you may think of, so don't be shy.
*-Unless you use it as a shoulder stock like I've been know to do from time to time.