Let's start with a story. Back in elementary school, I was sent to my pediatrician after a scoliosis check. I didn't have scoliosis (luckily), but my doctor asked how I wore my backpack. Of course, I had it slinging on 1 shoulder like all the other cool kids. What I didn't know was of the muscle imbalance I was creating. He said all I had to do was wear my backpack normally, easy enough to do.
That was years ago. But, I see women nowadays with gargantuan-looking purses like they're trying to rob a bank. It's fine to a certain extent, but I also see they carry a lot of things with them. I once remember my friend coming by my dorm and inside her purse was a laptop, bagel, notebook, pens, a spare tire, toaster, fish tank, etc. (maybe not the last few). That's simply way too much to be carrying all at once, especially when the load is not evenly distributed on your upper body.
So how do we fix this? Easiest way is to lessen the amount of items you have or do some type of resistance/weight training. The latter option makes you strong. Your muscles become able to handle the weight being applied to one side. Don't like the idea of lifting weights? Well, either way, if you want to have kids, how are you going to hold a crying baby in the future? Can't make that baby weigh any less no matter how many diapers you go through. In fact, they only get bigger, and uglier in the teenage years.
This post isn't just for women; it also applies to the one-strap bags men wear. Keep your body in good shape, it's not hard doing a change here, a change there.