I have lived in houses where previous owners have left piles of unused bathroom tiles behind. Small tiles are ideal as coasters. Take a piece of medium thick, non-fraying wool felt fabric, glue a piece under a tile, and cut the excess fabric when the glue is dry.
I used ordinary, water-based household glue and dark brown felt fabric. The tiles are easy to wipe clean.
I also made a couple of matching trivets. I bought simple cork trivets and glued four small tiles onto them. It does not matter if the tiles are slightly bigger than the cork trivet.
Cork and tile trivets are practical at dinner table and kitchen. I use bigger tiles under flower pots, protecting surfaces from water leaks or humidity coming through clay.
Making trivets and coasters is easy and fun, and it does not cost much if you can use spare tiles, for example, from your neighbours’ bathroom decoration, or tiles that came with the house, like mine.
If you want a a better finish, you could paint the sides of the tiles or cover them with fabric, cord or band.