Basic college chemistry
Alcohol: Dehydrating. Mostly works by being a certain percentage of your blood. Water, salt, and carbs are good for absorbing it out (Saltines are classic).
Caffeine: Dehydrating and very acidic. You’ll usually only have to worry about the acidity; tone it down with some milk (or soy milk, or toast, or...). If you use a lot, be careful to eat enough.
Tobacco: A stimulant. Make sure you eat enough. Frequent use worsens your immune system, so get plenty of vitamin C. Please know that your friends worry about you.
Weed: Lowers your blood sugar. Have a piece of fruit or some juice.