For the lack of file specified, you should just use the absolute URL for your link. As for converting products/ to products/coffee.html, that's ONLY possible if coffee.html is the DirectoryIndex (default file) for products/. Otherwise, Apache has no way of guessing what file in the directory you want served.
Have a read of the mod_rewrite tutorial linked in my signature for more information. THEN, if that's what you want, come back with a "specification" and I'll help you through it.