what's in my bag?

I've been experiencing soreness on my right shoulder lately. I feel that its mostly due to the fact that I fit my whole life into my bag everyday. I took out the contents of my bag and placed them on the table. There's nothing much in my bag actually, just my wallet, ID, tissue, alcohol, lotion, lip balm, and other small stuff. So, what is it that makes my bag so heavy? That is still a mystery to me. Maybe, I should just get a smaller bag, so I won't bring a lot of stuff every time I go out.