I rescued some credit card sized information "cards," made of a hard plastic just like credit cards , when the issue we had in our office was replaced by a new version and we were told to bin the old ones.
I took home a pile about 2 inches high. I drilled a hole through the stack in one corner and fitted a 2 BA nut, bolt and washer to hold them all together – with a bit of slack. I use the appropriate thickness of cards to make up a "pack" of the same thickness as the workpiece, swivelling the unneeded cards out of the way. And I use the pack on the other side of the vice as described in several posts above. I hope that's clear, the cards needed to make up the required thickness go between the vice jaws and the remainder sit just above or to the side of the jaws. All the cards stay on the bolt at all times so none get lost. It works quite well, cost almost nothing, and seems quicker to adjust than a screw jack..
Don't have to be plastic cards, could be small pieces of sheet metal all cut to the same size or even washers with an extra, off centre hole drilled in them.. Good use for off cuts?
Rod