Calcium hydroxide: It is for my mother to make prickles.
Potassium iodide: I need to get ready just in case some drop a dirty bomb in London.
Magnesium chloride: My son need magnesium supplements.
Just don't bring them as carry-on. Because some people may feel uncomfortable with all these chemical. Calcium hydroxide, for example, can do wonderful things on aircraft's aluminum frame, not to mention the ability to cause death/serious injury if you disperse it in a enclosed area, such as in the cockpit....
Check with US/UK custom.