Alcohol and Opiates don't mix well, they bring out each others side effects; you'll black out, probably vomit, feel sick, be nearly paralyzed during the "high". That is if you don't die. I've nursed a beer over an hour (not very tolerant to alcohol), and it floored me when I was only on a little hydrocodone (moderate tolerance). My alcoholic friend had a beer while on hydrocodone too (opposite of me, he rarely uses opiates) and felt like he was going to die. I just wouldn't do it, it muddies and dirties the high. If you must mixing a GABAergic drug with your opioid, then try a benzodiazepine. They are much "cleaner" than alcohol. You have to be tolerant to both, benzos and opiates though. Lower your opioid dose and take threshold effects dose of your benzo. It's still very dangerous and not recommend to beginners but not as bad as mixing alcohol with dope.
Caffiene mixing great. I drink a lot of green tea while I'm on dope, the heroin masks caffeine's negative jittery racing heart side effects. The only thing is I drink way more caffeine than I can handle sober when I'm high so the caffeine wds makes my heroin wds worse.