There are over 300 different societies and committees at Sheffield, as well as numerous sports teams (
here is a list of all the different societies, and
here are the sports teams). If you fancy volunteering (a great way to make friends and do some good at the same time),
Sheffield Volunteering offer over 200 different programmes for students to get involved with. Many (non-sport) societies also have their own smaller sports teams that play in inter-mural tournaments against other teams from around the university. This means that there is a great choice when it comes to activities at Sheffield, and there's pretty much something to suit everyone's interests.
To address your concerns about alcohol and bar-crawls dominating the society social aspect - as a former student at Sheffield myself, and one who was very involved in activities, I would say that this is not the case at all. For most people involved in societies, the society itself *is* the social aspect - it's about a group of people coming together to share a common interest. When societies do decide to meet outside of their normal meeting/ activity, the things they do tend to be pretty varied - in my society, we used to go for meals after every general meeting, run external training sessions, go to gigs together, go on trips etc., and I know that most other societies do this too. There is the occasional night out, but in my society I think there was only about three of these every academic year, and there were plenty of people who chose not to go along, preferring the other activities we ran. Every society also has a dedicated inclusions officer, many of whom champion non-alcoholic socials to make sure that every aspect of society life is accessible to all of its members. There is even a society, Lemon Fresh, that is entirely dedicated to putting on fun, unusual non-alcoholic activities for students.
If you want to get a good idea of activities at Sheffield, here's a
video made by the Students' Union. Also, if you tell me what you're interested in, I might be able to point you in the direction of societies that would be good for you.