Leung Cha literally means "cool tea"
leung = cool and cha = tea
It's a generic term for herbal tea. The ingredients may vary greatly. The composition of the tea may comprised of just one herb or a mixture of 2 to 100 herbal combination. The Chinese drink this mixture of herbal tea to fight off "the heat" accummulated in the body; such as after eating fried food or spicy food, etc.
It is hard to tell what is in it unless you are familiar with Chinese herbs and brew the tea yourself. Otherwise, there's no way to tell what is in there unless they list the herbs on the package.
The most common ingredient in "leung cha" is chrysanthemums "gok fa".

Thanks Rizz!