You can use broken beads, flatback rhinestones, paper and fabric scraps, and anything else you can think of! Here is a free idea from our Learning Center that shows how we embellished the tins:

http://www.artbeads.com/butterfly-flower-horse-gift-tins.html

The amount of seed beads in an 8 gram bag will vary depending on the size and shape of the bead. You can find the approximate number of beads per bag at the top of the main page for each of the seed bead categories. For instance, on the Toho Round 8/0 beads, you will see the approximate number of beads per bag (350) at the top of the page:
http://www.artbeads.com/toho-japanese-seed-beads-size-8.html