We have had a box at the O2 but would not bother again, the arena is so big that the artists appear small and you are looking at screens to get any detail.
Although there is a variety of places to eat queues form at most of them then the time to order and receive your food often means you have to leave your meal to ensure you see the start of the show.
each box has a reception area (where you are served burgers, pizza and beer) then about 4 rows of 8 seats at the front. You get a good view for something like tennis, but where there's a stage it depends where the box is. Dress code is relaxed but you do feel like royalty when you first get there and are shown to the private escalator!! posh toliets too!!
The boxes are relaxed and it's great skipping the queue to the VIP escalators. You won't necessarily get food though- there wasn't any when I was there. I think it depends on what the box owner has paid for. No waiters to bring you drinks either; we had to walk to the bar.
Boxes are decent, not snobby at all. I have been in 2 and both times, we could order [had to pay] food and drink at seat. They got the drinks from the bar in the suite itself which was nice. With food I think there was a minimum order of £20 each time, so best to group together. Although now, when I get tickets from American Express, you get access to the 'VIP' bar (box holders do too I think) and you can order some noodles they cook infront of you which are decent and good if only one or 2 of you are eating.
If you want to eat at a restaurant under the tent, get there v.early as its busy.
Re: parking, I have either queued for 90mins just to get on the A2, or last night for Peter Kay, within 20 mins of him walking off stage, I was out of the car park and on the A2 clear as anything.
There is a NCP at the tube station which is £3 on a Sunday, not sure what it is like though. Official car park is £20 if booked in advance, advice is, park near the exit, walk very quickly. If you are on the far right hand side [as you look at the stage] then you'll probably have a bit of a wait to get out as it is a long way to walk, but if you are on the left hand side, you should be able to get away quite quickly.