Hi FO. Have fun. You have put a lot of thought into this which is great. It's best to be over prepared than not at all.
When I was a young teen the girls I hung out with all started smoking marijuana. There were a bunch of times they offered but I always said "no thank you." Years later one of those women told me that she respected me saying "no" back then. That she always thought I was cool because I didn't follow the crowd. I never saw myself in that light at the time. Gradually I started hanging out with different girls who had interests more in line with mine as I saw that the focus on getting high wasn't conducive to having fun.
You will find people who aren't drinking. There will be thoughtful normal drinkers and there will be the massive partiers. You will still be fun. More so, actually. You'll remember what you were talking about. You'll remember to put on sun screen so you won't be suffering the next day from a dehydrated, sunburnt hangover. And you'll be happy with yourself. Be well