I've described this trick before. It starts with eggshells, about this time of year.
Every time you use an egg (if you were going to beat/scramble the eggs anyway), don't just crack the shell. Using a steak knife, chip a hole in each end about as big as your little fingernail. Blow out the egg and make your recipe.
Trickle water into the shell and rinse it out. Also, wash the outside of the shell with slightly soapy water. Set it aside to dry.
Repeat whenever you get the chance.
Around the time you buy the tree, also buy a set of watercolor paints, some different colors of glitter, white glue, and green pipe cleaners.
Cut the pipe cleaners in half. Make a sharp L-shaped bend at the end of each half-pipe-cleaner. Run one through the holes in each eggshell and curve the other end into a convenient hook. The L-bend will keep the eggshells from falling off.
Now paint each eggshell and hang it up somewhere to dry.
When they're dry, glitter them in gaudy patterns. Let the glue dry. Decorate the tree.
Voila! Christmas ornaments that vaguely resemble those glass balls, practically for free!
GentlyFeral