I will be attending my 27th AirVenture this year. I've been there every year since 1989 (where I first fell in love with the SR-71 Blackbird). I have found that for me that the 100-400 is the best/most versatile lens for the actual airshow itself. There is an incredible amount of static displays though as well so you will want to bring a wide angle lens as well. Here's the long version of a few things I would recommend for anyone looking to get nice photos from the show.
1) You will want to bring a folding chair with you since you will be sitting out near the flightline and it's just grass. That's really the only thing you NEED to bring aside from your camera, but some other things to consider are sun block, umbrella, water, portable power supply for cell phone, book etc. Carry ins are allowed so you can bring food and drinks in (no alcohol) along with coolers no larger than 18x12 inches. The umbrella is 2 fold as it works great for rain and blocking the sun. You may be sitting on the flightline for a long time depending on what you want to take from the airshow so it's nice to block that sun. I spend a fair amount of time on the flightline before the airshow so I'm always playing around on my phone and stuff so that's why I recommended one of those small power supply things for a cell phone. Certainly not for everyone, but for me it's nice to have. Anything to keep you busy is good to bring along.
2) Gates open at 7AM. You definitely want to be there by 7. I recommend planning to be there at 6:30 so that you can park and walk to the ticket counter to get your wristband. Even though you have a ticket you need to exchange that for a wristband at the gate entrance. If you plan to go multiple days you can get all wristbands (or the weekly wristband) your first day and then not have to exchange your tickets everyday. It's usually not terribly busy so the line is short and it's relatively quick as there are a couple dozen workers giving the wristbands out. Even though the airshow itself doesn't start until the afternoon you want to get there early so you can get setup in the front row which is best for photos.
3) Location. Once you get through the gate just keep walking until you get to the flightline area. Pick out a spot and set up camp. When you setup, keep in mind obstructions like the speaker poles which are newer in the past few years. These are tall and can be intrusive to your photos. So plan your location such that these poles are as far out of your photo panning area as possible. At the front of the viewing area on the ground you will see signs with numbers that indicate rows for aircraft parking. Behind you will then be lots of small personally owned aircraft. If you can setup as close to one of those signs as possible that is ideal. Throughout the day smaller aircraft will be pushed out down these "rows", so if you are near the edge of the row you won't have to move your chair as they push the planes down the middle of the rows. This is kind of important because if you want to get up and go checkout other stuff going on throughout the day and a plane has to get moved out they will take your chair and move it off to the side and they don't move them back. Easy way to lose your front row spot as other people then see no chairs there and move in. If you get up and leave your chair unattended you are required to fold your chair up and lay it down so it doesn't blow out onto the flightline or into aircraft. I believe officially you are not supposed to leave any chair unattended, but that has never been enforced. I always sit south of show center, but as Geoff alluded to if you go further south or north you can get some nice photos of turn maneuvers.
4) There are a lot of other things to take in aside from just the airshow so look at the website and all the special activities or stage forum presentations. One of my favorite things at EAA was 2 years ago when a number of SR-71 blackbird pilots held a symposium about what it was like to fly the plane. Funny group of guys with great stories and anecdotes. This year, for instance, on Wednesday evening Apollo 13 Flight Commander James A. Lovell and Command Module Pilot and Fred W. Haise will be speaking and discussing that mission, the issues, and the effort to save the crew.
