A Fremkit is effectively a desert survival kit. The Fremkit is a pack devised by the Fremen for servival in the open desert. With proper techniques, one can survive for weeks with this kit. Paul and Jessica used one when they were cast out of Arakeen. They were able to stay alive in the desert before they met Stilgar in his sietch. Since there is mention of such confidential matters as the riding of sandworms and the uses of melange in both food and manufacture, it was obviously not supposed to be shared to outsiders.