I agree with what others have said. Haven't made these recently but made them in Spanish class in high school. Brings back memories. Definitely crack them on someone's head... that's the best part!
Both of my girls made these in school last year, the teachers used shredded paper recycled from the paper shredder. It was also used at a friends birthday party. Definitely a great hit with all. Note: great idea for the leftover egg, make scrambled eggs or omelets
My best friend Jessica and I made these while in high school in the 80's. We dyed them like Easter eggs and smashed them on peoples heads (mostly guys;) We used a nail to make a small hole and carefully chipped a slightly larger hole at the other end and blew the eggs into a bowl. We had problems with chunky confetti so go with smaller cut confetti and you can use a piece of paper to make an adjustable funnel. These were also great for graduation parties and surprise parties. Lots of fun! Forgot to mention...we dyed them after we emptied the egg out, they were easier to submerge and get great color on. To let them dry both after blowing out the egg and rinsing clean and after coloring we used the empty egg cartons. Just cut off about 1/2 inch of the bottom of the little "cup" the egg sits in (in the carton). Close the carton and set it down with the cut side up and the lid on the table. The cut cups can then be used to hold the egg while it dries. You know birdseed would be a eco-friendly filler as well and very easy to handle.
So much fun! These were a favorite treat at my elementary school's Halloween carnival. If you are going to be using them outdoors, it's a good idea to fill them with paper confetti or shreds that will biodegrade.