The resurrected awaken on Riverworld with nearly-indestructible containers tied to their wrists, commonly called "grails", which produce food, drink, pieces of cloth, and luxury items, such as alcohol, tobacco, marijuana (and lighters for some), hair care utensils, makeup, and a hallucinogenic chewing gum, known as "dreamgum". To operate, grails must be placed onto large, mushroom-shaped "grailstones", found at intervals along the riverbanks, which produce an electrical discharge three times per day (corresponding to the times of breakfast, lunch and dinner). As agriculture is absent and impossible on the Riverworld, the grails are vital to an individual's survival, and cannot be opened except by its owner. Nevertheless, "grail slavery" is not uncommon, in which a person is held captive and the contents of his or her grail, retrieved by the owner, are taken by force by the captor. The slaver will usually provide the slave with enough food to keep him alive, as once a person dies their grail becomes useless.
Of special value are "free grails", originally found atop each of the grailstones as a demonstration of their relationship. Free grails can be opened by any individual, and as such, are valued for an extra ration of goods at each interval. In the history of Riverworld, several people have lost their original grails and sought free grails to survive.