I have to double-bag out of necessity. I have a lot of health problems, so I generally have to cart around a large bottle of water and some snacks and supplements, just in case I don't feel well. I have a regular shoulder bag for my "real" purse, and then I use a cloth bag with a local bookstore's logo on it for my second bag.

I take water, etc. with me to work. Also, my office is in the middle of nowhere and nobody sees me come and go. Double bagging is a necessity, and no one even sees my bags when I'm at work. I keep them under my desk.

I do not double bag for fashion, only necessity. The most common double bagging for me is when travelling or when I am taking my son out on a longer trip, and need to have child friendly supplies handy. I probably should think about getting bags that work together stylishly.