Polyethylene (HDPE) milk bottle (or similar)
A knife or scissors
A mortar & pestle
*If you're making fireworks you'll have some, e.g. KNO3.
Back then I could get sodium-chlorate weed-killer (it's broad-spectrum) where ~50% was just salt. You put it through a sive and the big-lumps are what you want.
Last time I bougts some the salt was caked onto the lumps like Nerds etc,,