I plan to go with a couple of friends and make it part of our holiday trip. We'll get there a week ahead of time and watch the stadium get put up and all the 100,000 seats and all that. Also, that way, we can maybe find a nice place to camp which is away from where most of the folks will be, yet semi-close to the Quidditch pitch.
We'll be 'backpacking' on broomsticks so will have the basics of stuff you put in a backpack, except that we'd also have saddle-bags on the broomsticks with extra stuff -- like our 'tent' and 'stuff' with which we don't want to do without. (The tent makers, Millamant's Magic Marquees has a special on tents for traveling. Ours is a 4 bedroom, 2 bath with a kitchen and sunroom.)
I don't know yet what I'll wear to the game. My friends are both fans of Bulgaria but ... I sort of like the Irish. But then, Viktor Krum .... *swoon*. So who knows! Actually, since I wear a lot of black (and some maroon) and don't often wear green, I'll probably just wear whatever I'm wearing and get a rosette to indicate what team I'll be cheering for!