The other day I was sitting on my bed reading with a cold drink when I realized I needed coasters for the bedroom nightstands. I still had a whole bucket of flat beach stones left over from the mirror I made so I decided to use them to make pebbled coasters. That way they coordinate with the mirror and are cohesive in the room.
I bought small round cork pads (for use under planters) and affixed the stones to them using a hot glue gun. In hindsight I should have painted them black or grey first because the cork does show through between the stones and on the edges.
I was concerned that they would be unstable for glasses, but the pebbles are surprisingly uniform and keep the glasses and bottles I tried out quite level.