I've had two proper nappy bags, but I'm one who doesn't carry a handbag anyway so I wish I had never bothered. My Oioi hobo bag doesn't look too dissimilar to a big handbag, but I could have saved a motza by buying something else. I'm not into that whole cutesy baby thing so it wouldn't really have mattered whether it was a true nappy bag or not for me.
Like SS I just have the basics in a small bag in the back of the car. If we go somewhere longer obviously I take more, but you learn pretty quickly what's manageable for you.