Racks used in MACs have been put into sets which go something like this:
Short quickdraws (6)
Long quickdraws (6)
Screwgates (5) Note: one screwgate may be replaced with two snapgates
120cm slings (2)
This is just a guide and each rack is slightly different. There's always other gear kicking around if you think you'll need it.
If you're ever unsure of what should be on your rack, ask a member of the commitee or a competent leader.