The "must-haves" for every coral keeper?

[mandyplo]

What are some of the crucial supplies that you guys think every coral keeper should always have on hand? From foods to treatments(dips) to propagation, if you've personally found it useful I'd love to hear about it. Experiences with products, benefits, how it has helped/saved you (or your coral) and anything else you'd like to share about it please do!

Brand/product names are preferred (as opposed to just a general chemical or nutrient)