Yeah the paracetamol thing is fine. Pop in there before if you're unsure, but I didn't know where it was and I've been successful in getting a job at Boots twice now. They'll probably also get you to hand out baskets...just smile and do it (you'll probably never have to do it if you work there). I went to a meeting where we were told the bosses (ie of the whole company) said they were going to change the interview as it isn't that great, but I think they still do it. I mean they literally mark you on those simple tasks.
They'll ask about why you'll want the job, I've always said money and also because of the experience. They might also ask what you think you'll offer to the store, just be confident.
I've only ever done weekends too, and tbh, though I rarely ever shop in Boots it's good working there. They train you up and the pay is good, and for a first job in retail it's well respected.