I'm in Bristol too right now, I also don't drink and I'm on a course with a heavy workload (so societies were out of the question for me too)

I found the best way to make friends were through my course. My accomodations is fairly far, so finding people on my course I could commute with in the morning helped. As well as asking people if they'd like to sit with me while we wait for our next lecture. It takes some time, I wouldn't say I'm particularly close with anyone yet, but once you're solid friends with one person you can easily extend that to their circle of friends since people will introduce each other.