I have to admit that when travelling I take usually 4 or 5 cameras. I choose them depending what I want to photograph. At first, I used to put them on my shoulder bag, but the main problem is that they can be damaged, or is quite difficult to take the camera you are looking for. On the other side, the classic Lomo bag allows you only two small cameras...
The solution came when my girlfriend (once she assumed that I don’t have enough with one camera) give me as a present a professional camera bag. Mine is a Lowepro Mini-Trekker-AW. It is designed for a slr camera with lots of additional lenses. It’s very rough, very good quality, and protect perfectly well your most valuable goods.
Well, I use it in a quite different way. Instead of taking one camera and all its accessories, I take 4 or 5 cameras, and some accessories. It has some pads provided with Velcro® that allow you to make the camera compartments size at your choice. In addition it’s rain proof.
The advantages are that’s very solid, versatile, and protect above all your cameras.
The drawbacks are that’s quite expensive and a little old fashioned.
In conclusion I can’t travel without my Lowepro and my loved Lomos.