Not to be confused with 'caution', although it is the same word. Kaucija is the charge for the packaging, most often the returnable bottle. You return the bottle and get the money back, or take another bottle.
The bottles for which it was charged were the standard beer, milk, yoghurt, wine and mineral water bottles, which could be re-corked. The bottles for stiff drinks like vinjak, however, have a screw-on stopper and weren't priced.
Nowadays you can't find milk nor yoghurt in a bottle, there's no standard beer bottle (it seems that most of the manufacturers have their own bottles, often several types of), about half of the beer bottles are non-returnable.