Holidays and special occasions such as the 4th of July, Christmas, and New Years just to name a few are often big occasions and festivities to drink alcohol and consume other types of recreational drugs at parties.
The first option is the simplest, which is to not attend the party or visit family that will encourage drug usage or drinking. However, you cannot just lock yourself in a room and forgo living life. What a person in this situation needs is support and a potential out. Prior to attending advise the person inviting that you have another engagement and can only stay for a short time. Also, take a friend or date that you trust enough to help you stay sober. This person can also be your excuse to leave.
The holidays with friends or co-workers often involve meeting at bars or restaurants that service multiple types of alcohol, not just beer and wine. When you attend one of these events hang out with those who do not drink. You can offer to be the designated driver as well which is another way out of the situation if you don't want to tell them that you are an alcoholic. Choose a non-alcoholic beverage such as soda with cherries or lime to make it seem like you are having an alcoholic beverage. Or, drink an energy drink which in many rehab programs is not advised after being in public. Yet, I drink certain energy juices on a daily basis and at least one energy drink on the weekend.