The sandpit have a ton of stuff, 2 snatch landrovers, a WMIK, the DAF truck, a RM snow trac, the 432 and some wheeled APC thing I can't remember the name of. Oh and don't forget Dora the explorer and the Quads which are mostly used by the marshals. There are also people who bring along their own vehicles for Milsims, some have been heavily adapted. Like there is a camo 4x4 van thing with a turret type thing.
Rules for getting in the snatches is pretty easy, if you fits you sits. If you can get your hands on a M249 and want to be ragged about in the top cover for the snatches then go for it but honestly my back is still protesting about that one. Depending on how Andy is feeling and how the vehicles are behaving there is a pretty good chance they are out on normal skirmish Sundays.
The ribs belong to someone else (Stirling I think) who often use the pit for their Milsims, if they hang around for the Sat night and there is a Sunday skirmish they sometimes get them going then as well.
As far as I am aware the Helicopters that sometimes get used are always transport infil/extraction and there are really strict rules about not fireing from them or at them. It would be really easy for a stray bb to do damage and cause a crash so not quite the super exciting gun fest you are probably expecting.