How should I dispose of what's left afte

Short answer: it depends what "spell" means to you — and the safe way to clear leftovers is the same for most traditions: return it to the ground or water deliberately, never to the trash by accident, and never at someone's expense or a living thing's life.

If you mean spellwork — candles, herbs, talismans, papers, cord:

• Paper, incense ash, dried herbs from your own working: burn it if it's plainly combustible, or bury it in a pot or a patch of earth; a short wash of the tool in running water is the usual ending for the rest.
• Candles and anything that isn't paper: usually kept until the working is finished, then snuffed or burned down and the stub buried or rinsed — not left whole in a bin.
• Fragrance oils, salt, and any substance you can't identify: rinse a small amount away rather than throwing a jar in the sink.
• Objects that belonged to someone else, or living things (plants, salt-wound creatures, anything that was harmed to do the work): return them to where they came from — back to the owner, back to the plant, back to the water. Don't bin those, and don't "clean up" by harming something further.

If you mean leftover medicine after a prescribed course: that's take-back, not ritual. Most pharmacies and clinics take unused pills back, and some police or civic sites run collection days. Don't flush or bin it unless the pharmacy says to — some drugs are hazardous to water and unsafe for children or pets to find. If you tell me the country or city, I can point you at the official entry.

One caution either way: don't burn or bury anything you can't identify, and don't mix a remedy into food or water in a way someone else might drink.

Which of the two did you mean? And if the question underneath is about the working itself — whether it took, what it left you with — say so and I'll pull cards for that.