Wine with soda water. Something you can drink slowly or not, but will take you through a long evening without getting you under the table.
There are different schools on how to make it. Old school says the soda water should be made on the spot, i.e. you need a syphon bottle, not prepackaged soda water. Others allow that, as these bottles aren't that easy to find, and carbon dioxyde cartridges are scarce. There were tradesmen who'd rent the big, 40 liter bottles and carry them around for you, but it's been 15 years ago when I saw the last one. Finally, there's the most relaxed school, which allows mineral water, which is at least always available.
The other point where schools differ, is whether you pour water or wine first. For the hardcore syphoneers there's no doubt: you need to master the technique of hitting your wine with a precisely measured squirt from a standing bottle. With bottled water, however, the opinions differ. There's a school whose motto is "are we spoiling the wine or mending the water?", i.e. water first, then make it better by adding the wine.
The ultimate tavern bench tearer (literal translation of "kafanski klupoder") orders a nameštaj (furniture), which consists of two small (0,5 l or 0,25) pitchers and a glass, so he can mix the wine and water at will (and also under his own control, so he knows how much water is there in his špricer).
And, finally, there's the endless matching game. One runs out of water, has wine left orders more water. Then he runs out of wine, has water left, orders more wine...