I would say, hands down, buy the wristband. I didn't drink until I got to uni but decided to buy the wristband anyway. Of course you don't need to drink and no one will force you to drink but I'd encourage you to do so. Get to know your flat mates, socialise with them just have fun. Just for a week, leave your worries behind and just have fun. STYCs will be there to make sure you are safe and are having fun. Freshers week is still the best week of my life, got so many good memories from it. It's a once in a life time opportunity, please don't miss out on this cause of money.
As for day time event, you should be able to the them without the wristband, they are only really for getting into clubs. What lectures do you have in freshers week? I think they only have induction activities at the department in freshers week but I might be wrong. Either way, they are not that important.