This is tricky, but basically, "stick" is the unit of butter, dynamite, chalk, gum, etc., that is most usual.
This works for your examples (but "thin branch", not "tin brunch"). But I'd never say "stick of chocolate"; a piece of chocolate can be almost any size or shape. Also I don't like "stick salami," I suspect it's an error; I'd say "slice of salami."
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