For folks who like to frequently drink out, many bars will keep a bottle of Sake (rice wine) for you with your name on it - this is called "Bottle Keep" . They throw it out after a certain period if you don't come back to drink it all though.
Customers can feel like a regular as they go back to the same place to drink and they don't even need to bring along any cash either as they have already paid for the bottle.
This also means that customers don't feel pressured to drink the whole bottle just because they've paid for it and encourages customers to buy expensive bottles too.
I don't drink at all so don't know if this is a Japanese custom or a worldwide one?