The pattern is shown in small and large, but you can make them any size in between just by increasing more for the base and making the sides longer. The best part? It's almost all single crochet.
What you need
Medium-weight cotton or cotton blend yarn — the small bag is about 40 yards of Lily Sugar & Cream in color Pebble; the large bag is 145 yards of Lion Brand Cotton Ease (original, which has been discontinued) in color Terra Cotta
size H/5 mm crochet hook
stitch marker (optional)
yarn needle
Gauge: 11 or 12 stitches per 4 inches/10 cm (green was 11 and orange was 12) in single crochet. Gauge is not that critical, but you want it to be somewhat firm.
Size: small bag is about 10.5 inches/26.5 cm around and 3 inches/7.5 cm tall with a base that is about 3 inches/7.5 cm across. Large bag is 16 inches/40.5 cm around, 10 inches/25.5 cm tall and has a base that is 5 inches/12.5 cm across.
Instructions
For both sizes, make a slip knot and chain 6. Join the chain into a ring with a slip stitch.
Work 6 single crochet into the ring. Join with a slip stitch. 
*SC1, SC twice into the next st. Repeat from * around, joining with a slip stitch at the end. 12 sts.
*SC in the next 2 sts, SC twice in the next st. Repeat from * around, joining with a slip stitch at the end. 18 sts.
*SC in the next 3 sts, SC twice in the next st. Repeat from * around, joining with a slip stitch at the end. 24 sts.
For small size, work a single crochet stitch in the front post only around, joining with a slip stitch at the end.
For large size, continue working base in the same manner, increasing 6 sts each rnd with 1 more st between increases each rnd until you have 60 sts, then work a round in the front post only.
For both sizes, place a stitch marker if desired to mark the end of the round and begin working single crochet in the round until your piece is almost as long as you want it. For the small, that’s about 2.75 inches/7 cm, and for the large about 9 inches/23 cm.
For size small, chain 1 and work a half-double crochet in each stitch, joining the round with a slip stitch at the end.
For large size, chain 2, skip the first SC and work a double crochet in each stitch, joining the round with a slip stitch at the end.
Size small, work one more round of single crochet; size large, 3 rounds. Join with a slip stitch at the end, cut yarn and pull through. Decide which side you want to call the outside and weave in ends.
To make the strap, chain to your desired length. The small one is 3 feet/1 yard long, while the large is 6 feet/2 yards long.
Thread the strap through the larger crochet stitches to make a drawstring.
If desired, tie or sew the ends together to make a strap.
Very cute idea. My 3-yr-old grandbaby will love these. She loves to pick up pretty rocks and shells. These will be a very handy thing for her to have! I’ll be geting out the crochet hooks and leftover yarn this evening!