I did an experiment with this
I've had a few benzo + alc black outs:
What my process ended up being was id PLAN to have 1mg of Xanax, and 2 beers.
Id take the 1mg pill
Drink two beers
And suddenly lose all control of common sense and second thinking because I was so messed up.
I would end up slamming tons of other drinks and popping 2-3 more pills.
This exact process honestly happened 2-3 times
I tested this and gave my friend 1mg Xanax and some alcohol to see how he'd be, he was very chill and felt great except for the fact that I had to hold him down so he wouldn't grab the bottle. This is even after he told me he wasn't having more than 2 drinks and 1mg
SUMMING THINGS UP
It's OKAY to have one drink if your benzo amount is low for you, but honestly id get a babysitter to make sure you're not doing anything dumb.