One of the few Mystic Codes carried by El-Melloi II. The tobacco inside was specially put together by El-Melloi II himself. There are many varieties, from those used for defence, for setting up Bounded Fields, for stabilizing the mind, and for activating Magic Circuits.
As to why he decided on cigars, after being forced into the position of El-Melloi II, a panicked Waver Velvet was searching for some way to make himself look more Lord-like, to which some drunk magus mentioned that “A cigar and a suit are a man’s weapons.” Or something like that.

Lord El-Melloi II Case Files material: Lord El-Melloi II Case Files Glossary