Don't no about the alcohol but the coke will its the the in it that will show up
Why in the world would your boss want a stool sample? That's odd.
If this is a drug test, and you've used a drug, the best policy is to be honest rather than trying to get away with lying about something.
If its a drug sample a urine test or hair follicle test would usually be the test of choice. It's extremely odd for a stool sample to be tested (as nurse girl said) for alkaloids such as cocaine since its excreted in urine within 2-4 days of use. Again as nurse girl said, honesty is definitely the best policy about these sorts of things.
A stool sample? That's just weird.