So tell me- what is and is not supposed to go down a garbage disposal?

Growing up, one always had to put things in the trash. Everywhere I've lived for the last several years comes with a disposal- and I've gotten more and more lazy about pulling things out of the sink.

Tonight I made dinner and put beet skins and ends, shallot skins and ends, and egg shells down the disposal. Well they made it through the disposal, but completely plugged up the pipe. Both sides of the double sink were completely plugged (in fact when I would turn on the disposal, it would shoot everything from that side of the sink up through the other sink, spraying debris all over the dishes that were drying on that side). Eventually I figured out how to open the bottom of the pipe and was eventually able to clean up the mess and now I have a functioning sink again.

Initially I was thinking the egg shells were where I went wrong, but it seemed like the shallot skins were doing more of the plugging. Any thoughts?