Step 1: Materials List
Plastic or plastic coated cups to mix in
Something disposable to mix with (I used popsicle sticks)
A well ventilated area
Bottle caps to set in the resin
If you want your coasters to be colored, you can get resin dyes as well.
Links above are just some places that I have found these items, not necessarily where I got them from.
Step 2: Get a Mold and Prep It
To prep your mold, spray a thin coat of mold release on your mold. Let it dry before casting your resin.