Salty and spicy foods make you thirsty.... so you'll be buying something to drink.

Peanuts and popcorn are salty, so you're more likely to buy something to drink.

Bars, restaurants and other types of watering holes offer complimentary snacks such as peanuts, pretzels and even popcorn for three reasons: #1: The obviously salty snacks make a person thirstier so, in turn, they will drink more. #2: Alcohol also tends to make one a bit hungry. Some folks are turned off by "bar food" i.e.: fried foods, hamburgers, nachos, etc. so they would be more likely to leave when the pangs hit them. Others know their S/Os would kill them if they didn’t come home for dinner hungry. Having a little something to nosh on ensures the establishment, at the very least, a beer or two more added to their bottom line. Which by the way, only adds up to about 50-75¢ profit when all is said and done. #3: It's just darn good customer service. A majority a people today will not drink tap water, me included. The business has to purchase bottled water and so turn, must sell it to regain their cost, plus a profit. While it is not an alcoholic beverage, it is a beverage all the same and will always be treated as such. A few bars that I used to go to would have a cooler of water with cups beside it at the end of the bar, to serve yourself. When the bartender serves you ANY beverage, you are still being served. Peanuts can be purchased in bulk and cost well, just peanuts. Bottled water, on the other hand, does not.