On Saturday/Sunday, you should definitely head to RWY 9/27 (at the north end of the field) to watch the mass arrivals for a little while. It's pretty awesome. Even better if you happen to have a portable radio that picks up the aviation frequencies. The (usually) organized chaos is a treat to watch.

Sunday is a little bit tough to hit the booths/displays because the vendors are trying to get the final touches done for setups. Then there is always the opening keynote at the Theatre in the Woods.

Definitely look at the airshow schedule (on the EAA Airventure site, news section) to decide if you want to spend the late afternoon on the flight line. You can make a judgement call if there is anything in particular you really want to watch.

Otherwise, you should DEFINITELY spend time in Warbirds. There are BUNCH of planes up there. It's toward the north end of the field, so you can either hoof it or take a shuttle. For early jet age stuff, check out the Mig behind one of the older buildings near the flight line, show center, near-ish to the control tower. (Someone here will correct me and mention the specific building.)

In terms of where to set up, if you arrive late Saturday/early Sunday, you'll have a walk to the airfield for sure. Keep in mind that the check-in office closes (as does the gate) at midnight. So if you get there at 12:15, you'll likely be sleeping in the parking lot.