What should not go in the garbage disposal? American Home Shield put together this list.

• Coffee grounds. Coffee grounds can clump together into a thick mass that will clog your food disposal and won’t allow your sink to drain.
• Meat. Does your garbage disposal stink? It might be because you’re putting meat into it. You should never put meat into a food disposal sink. It can stick to the interior of the machine, rot, and cause a stench. Always throw meat remnants in the trash. Bones (with the possible exception of those from fish) should also stay out of the garbage disposal. Your unit isn’t strong enough to grind them up.
• Starchy foods. Putting bread, oatmeal, pasta, and rice in your garbage disposal is a bad idea. These foods expand when wet, which can form a gelatinous paste in your drain and block up your sink. 
• Shells, nuts, and vegetable peels. The shells of seafood and other crustaceans are also things not to put in a garbage disposal. The little bits can dull the blades and clog the machinery, causing the food disposal to malfunction. You should also avoid eggshells, nuts, vegetable peels, fruit cores and pits, and corn husks and cobs.
• Grease, oil, or cooking fat. These materials should never go into your plumbing, whether you have a garbage disposal or not. It can solidify and cause a whole mess that an expensive plumber will have to sort out. 
• Fibrous foods. Some examples of fibrous vegetables that can’t be ground up include pumpkin, celery, kale, lettuce, chard, artichokes, asparagus, and rhubarb. Their stringy materials can tangle up inside the unit and jam it. If that happens, you’ll need to unclog your garbage disposal.
• Non-food items. We’ve all experienced flipping the switch and hearing the grinding of a fork or spoon we missed. It can also be easy for a stray napkin or food wrapper to sneak its way into your sink food processor. Try to remember to do a quick check before turning on the appliance. 
• Caustic cleaning chemicals. Avoid harsh chemicals like drain cleaner and bleach. Instead, use natural deodorants for your garbage disposal, like baking soda, vinegar or lemon juice, and dish soap.