From Monkey Island wiki
The Grog Machine is a recurring prop from the Monkey Island series. During the first game, The Secret of Monkey Island, it is located at Stan's Previously-Owned Vessels. Guybrush can put pieces of eight into it, but nothing ever comes out. At the finale of the game LeChuck punches him into the Grog Machine, and a bottle of root beer falls out of the machine, which can be used in place of Guybrush's lost ghost-destroying voodoo anti-root to defeat LeChuck.
The grog machine appears again in Monkey Island 2: LeChuck's Revenge during the finale of the game. While walking around in the underground tunnels looking for materials for a voodoo doll to destroy LeChuck, Guybrush finds the machine gathering dust in an old room. If he uses the coin return, a piece of eight flies out which serves the purpose of distracting LeChuck to get his underwear.
The grog machine returns for Escape from Monkey Island, once again at the shipyards, which are now run by the Harbor Mistress. As before it will not dispence any grog when Guybrush uses it, although if he kicks the machine a pile of cans will eventually fall out. This Grog Machine has decidedly different design, being green and dispensing cans of grog rather than grog-bottles.
The grog machine also returns in "Rise of the Pirate God" in Tales of Monkey Island. According to the Ferryman the grog-machine is for "the thirst of eternal waiting." Guybrush can use it to get change to pay the Ferryman and to get some "liquid courage". (In the PS3 version, using a whole eight in the machine and pressing other grog-labeled buttons prior to pressing the one for liquid courage earns the player a "Grog, Grog, Grog!" bronze trophy in the "PlayStation Network Trophy Achievements".)
- According to LucasArts designer Noah Falstein, the grog machine was originally considered as an opportunity for product placement.<cite_reference_link>
- According to Ron Gilbert the design of the Grog Machine had to be altered somewhat because the the Coke wave was also copyrighted.
- In The Secret of Monkey Island it is possible to get stuck in the game, unable to continue the adventure further, if the player uses all of Guybrush's money in the grog machine.