Charm packs are perfect for making quilted coasters - and Oh Deer by Moda makes them modern & bright. Total items needed are 5 charms squares and a piece of fusible fleece 4x4" or batting for each mat.
One charm pack makes 8 coasters with two scraps left over - not bad. They wash well and stand up to heavy use. A little fiddly to get all the triangles to nestle tightly together - and this is definitely where pinning helps as you sew.
There are loads of tutorials on how to make these sew and 'turn' coasters. Pat's Patter is a good place to start for picture layout.
Here are my suggestions & additional comments:
1) Absolutely use fusible fleece or batting for a little more weight on the back square. If you only have regular fleece and no fabric spray - you can sew an "X" through the back square only - this will latch your fleece or batting so it won't move when you 'flip' the coaster inside out.
2) If you are fussy like me, 'design' your coaster how you want it to appear ... then FLIP it over (and nestle it back together again) and sew your coaster with the wrong triangles images visible to you.
The images you see on the fabric just before you sew all the layers together are NOT what will appear when you turn the coaster inside out.
3) Use a small stitch and trim sides/corners. I usually sew off the coaster after each side but do a few reinforcing back and forth stitches at the corner area. After turning the coaster inside out - I use a chop stick to make the corners pretty.
4) Lastly - its personal choice whether to top quilt them - I say 'yes' as they tend to flop & not look finished. How to do it in one continuous line is shown (a little rustic) below.