Just remembered I went to watch the English Intermediate comps there a short while back. Quite a low key venue and no cafe as the others have said. But most comps have a host club, who raise money by selling some simple refreshments, but I don't know if you want to rely on that. They had tea and coffee and snacks I think, but you weren't allowed to take drinks in the viewing area.
Most people tried to park at the front, which is on the main road, and this was heaving. As was parking at the rugby club next door. We turned up Greencoat road (a side road just before the school) and about 100m up there was a big car park behind a chain link fence - sort of at the back of the school. There was loads of room in there. We made the mistake of trying to find our way through the school buildings from the car park though and got horribly confused, so I would walk back around to the front of the school and go in that way (around to the right of it).