whats in the cargo holds?

Have seen lots of discussion about the freighter and the "freightees"- 
haven't seen any discussion about the freight.

Whats in the cargo holds?  Why do they need a freighter to "rescue"? 
Obviously its because there was no rescue.    So why do they need a 
freighter?  Are they carrying weapons?  Soldiers in the hold? 
Scientific devices?  Or do they need the cargo hold to remove "stuff" 
from the island (whatever the stuff is thats worth removing)?