As long as it doesn't become a common occurrence, it may be okay to have a drink or two while on amitriptyline if you respond well to the drug and talk to your doctor about it.
I got my doctor's permission to have some champagne on my sister's wedding even though I was on amitriptyline. He said that since I don't experience any side effects of the medication and I won't be drinking much, it's okay for me to combine them just that one time. But he did have me lower my dose and take it early in the day so that there was at least eight hours in between the medication and the alcohol.
I didn't have any problems though, everything was great and I continued back on my regular dose the next day.