Grog Machines were vending machines that supplied variants of grog and Root Beer.
One could be found at Stan's Previously Owned Vessels. A damaged specimen (perhaps the same) was found in the tunnels under Dinky Island.
In The Secret of Monkey Island, it is possible to spend all of your money in the vending machine at Stan's Emporium, thereby making your game unwinnable, since you will then be unable to buy the sword, the shovel, or the treasure map.