There are some great alternative uses for them.
In the kitchen, you can slip a coaster under oil and vinegar bottles that you keep near the stove, it will keep the counter clean and catch any drips.
speaking of catching drips, slip a coaster on your stovetop and use it as a spoon rest to catch drips and keep the stove cleaner. They also protect counters and tables from hot pots and pans.
Wedge a coaster under a furniture leg on an uneven floor to make sure the piece isn't wobbly.
If you have a coaster with a lip on it you can use it for a soap dish in a small bathroom.
You could also line up coasters on a tabletop or sideboard and use them as bases for pillar candles.