Is it OK to use coffee or other drinks to clean road rash?
Plain black coffee would be okay; it's just water and it should be nearly sterile.  However, I would definitely avoid coffee that contains milk, sugar or other additives that can support bacteria growth.  

Now, this is going to come as a bit of a surprise, but what is an excellent wound cleanser is urine.  Yeah, yeah, I know.  But other than the ewwww factor, it's nearly perfect.  It's warm, sterile*, and near isotonic.  Naturally, the guy's not likely to agree to let you urinate on him, but he can do it himself.

*Assuming the person is healthy.