Starting with the Generation III games, when purchasing a drink there is a 3% chance that the player may also receive an extra drink for free. When this happens, the message "Score! An extra can of [item] dropped down!" or "Bonus! Another can of [item] dropped down." is displayed, depending on generation. In Black 2 and White 2, there is a Medal for having this happen.
Although vending machines are listed as dropping a can of the drink in question regardless of game and generation, the item minisprites depict only Lemonade coming in a can. Fresh Water, Soda Pop, and Moomoo Milk are depicted as bottles in their item minisprites, even if bought through a vending machine which says it drops a can.
Out of the items sold in the Department Store vending machines, Fresh Water is the best deal from a $/HP comparison, at $4/HP. Soda Pop is the worst deal, at $5/HP, and Lemonade is in the middle, at $4.375/HP.