Here is a very simple coaster pattern that can be whipped up using your leftover yarn. I used Red Heart Comfort, but any heavy worsted weight yarn will work.
The finished size is 4 inches across, making it great for use as a scrubby as well. Or, since it has such a pretty lace, you could also use it as a cool doily for small candles.
And since you only require such a small amount of yarn, you could crochet this coaster in all sort of vibrant colors to keep for yourself or to give as a gift.
Material: Red Heart Comfort, (or any yarn desired)
Hook size: H/8-5.00MM
Finished size: 4″ square
Ch 4, join with sl st to form ring.
Rnd 1: Ch 1, 2 sc in each ch around, join with sl st. (8 sts)
Rnd 2: Ch 4 (counts as first tr), work another 2 tr in same st, (dc, ch 2, dc) in next st, *3 tr in next st, (dc, ch 2, dc) in next st, repeat from * around, join with sl st. (20 sts and 4 ch-2 sps)
Rnd 3: Sl st into next st, ch 3 (counts as first dc), work another 7 dc in same st, ch 2, sc in ch-2 sp, ch 2, *8 dc in center tr, ch 2, sc in ch-2 sp, ch 2, repeat from * around, join with sl st. Fasten off.
You might also enjoy the following:
Slanted Puff Stitch Dishcloth, Placemat and Coaster Set
Little Dots Coaster
Crochet Flower Coaster