How about a pitcher?

If a table orders two glasses of wine, two draft beers, or two margaritas - offer the bottle, or pitcher if it's an option. Sell it with - "If you think you might have another drink you guys should think about a pitcher - It's like getting a free drink."

Usually you get 5 drinks from a pitcher or bottle of wine and the it usually costs about what 4 go for on their own.

You are looking out for the client - and can save them if they are going to drink a bit, and if they are on the fence you might persuade them to have a little more. They almost always will finish the pitcher and then be glad you saved them the money. You facilitate them having a good time and they tend to favor you at the end of the night.