1. They only really cared about you videotaping matches on the final day. I saw a lot of people break out their video cameras and tape black belt matches on Saturday, and nobody cared. It was only on the day of the finals that they started searching bags. I did not video any matches after Thursday (the only day that it was officially allowed), partly because I didn't want to have my camera taken away or something, but I was also still wallowing in righteous indignation.
2. If you're there with friends, excellent. But if you're there on your own, don't bring more than 1 bag, the room is just too huge and you won't be able to keep an eye on your stuff the whole time. Also, if you have to go to the bathroom or buy some food (see next) you will have to lug your stuff everywhere with you.
2a. Travel as light as possible. Leave extra space in your bag for food, maybe an extra T-shirt and maybe a couple of DVDs that you may or may not (you know, inevitably) purchase.
3. Buy extra food and water in advance. You don't want to be starving but afraid to leave your seat. This scenario will usually take place in addition to one of the following circumstances: either there's nobody in line at the concession stands but there's a hugely important match coming up, or there's a lull in the action and everybody wants to get a hot dog. Buy extra food in advance. Bring your own water though.
(note: the hot dogs at the Walter Pyramid were in my opinion incredibly good, I didn't try the pizza though)
3a. If you're interested not in the regular food, but the açaí, then you don't have to worry, as the stand for that should be located in an area with a good view of the mats. They may change the location for next year but I honestly don't see why they would, as it made it so much easier for them to sell their product. Which was fantastic.
4. Bring a bit of extra cash but leave the credit card at home. If you're anything like me you simply won't be able to walk past the DVDs and not "have a look", no matter how many times you do so.
5. Are you competing? Get there early on your first day. If you do not, then the line to collect your competitor T-shirt may take 30-60 minutes to get through. Why? I don't know, it seems like it's pretty straightforward: say hello, tell them who you are and show your ID, collect your stuff and go away. Someone will always manage to drag this process out for several minutes.
6. If you are a competitor but you only see action on some of the days, you will be able to enter as a spectator for free (normal spectator fee is $10), which is nice - just go through the athletes entrance, EXCEPT on the day of the finals. Be aware that on the last day everyone except black belt competitors has to pay a $15 entrance fee. I was a bit shocked at this. I understand why they did it, which still doesn't make it OK, but whatever.
7. Bring an iPod. Mundials competition is a huge game of "hurry up and wait", and trust me, the waiting you have to do will be excruciating. It's MUCH better with friends around but it's nothing short of torture if you have nobody to talk to.