When you mix cocaine and alcohol you get cocaethylene which is more toxic to your heart than either of the two alone. Alcohol is best avoided if you're doing cocaine.
Impotent or mediocre coke isn't worth the money. To get a true cocaine experience your shit has to be pure. A lot of the 'coke' out there is mostly ephedrine and speed with procaine or lidocaine, it is cheap and feels dirty. Good coke generally comes rocked, as it is hygroscopic, and in direct light should be glossy like fish scales.