It really depends on what you are eating

Barry has mentioned a pretty good setup if you are just doing
dehydrated "Freezer Bag" style cooking with just boiling water - using two homemade alcohol stoves.

If you are doing more "complicated" cooking you might need more.

Me, I also tend to ususally do things like Barry - alcohol stoves and a couple of pots. I have also done well for four people using a large 2 litre anodized alumium pot from antigravity gear, along with a snow peak gigapower canister stove.

http://www.antigravitygear.com/proddetail.php?prod=MKBANS

is the set I have which would do fine for that. I normally use only the small pot when solo and add the big pot for a group.