We bought this bag --
http://www.target.com/SwissGear-Vertical-Travel-Black-Grey/dp/B001QSYEJ8 -- for our WDW trip. I bought a bag because I have a black leather fanny pack that I love, but it's getting old and the plastic waist snap keeps falling open whenever I bend over or sit, which very much limits my fanny pack's usefulness!
We have begun calling the new bag the Swiss Army Tardis Bag, because it's a whole ton bigger on the inside than it looks. I guess most folks use this bag for their computers or whatever, but it's perfect for the two of us. It's actually called the Swiss Gear Vertical Boarding Bag.
We don't have children, but we will be carrying bags of nuts and beef jerky, two bottles of water, a digital camera, our cards (including the hotel key, DL, etc), maps of the parks, fast passes, and other paperwork -- and the bag is STILL big enough for extra batteries, our mini-dvd camcorder (and its extra battery and extra new dvd's), pens, some cash/change and a couple of ponchos on top of everything else, *and* if I wanted to, I could STILL put paper on the back of the bag (the back of the bag has pockets!) and an Ipod in the front. I won't do that, though, because stuff in the very front and very back would be a lot easier to steal.
The bag itself is a nice size, I'd guess about 10" tall, 6" wide (all the way open) and perhaps 8" across. It has one of those wide things with some soft fabric underneath on the strap, so that it won't cut into my neck. In color it's grey and black, with red accents here and there and the Swiss Army symbol on a small shiny enamel (probably, it could be painted metal) button right in the middle of the bag. It will easily fit in a small locker or to my side on a ride.
Tested it in the rain today and while I wouldn't call it water*proof* it was certainly water resistant.
I like the fact that I can lock the bag shut with a carabiner clip and also hook it to a belt loop on my pants, thereby making it secure if I go on a ride, and safe to deter theft.
The bag has a very long shoulder strap (I adjusted it all the way down to see how far it was, and it went to my knees while I was wearing it cross-body -- I'm 5'3" and, er, well-endowed! So it should fit just about anybody) and a carrying handle on the top.
I like the rugged materials, they seem pretty durable to me. Best of all, Target had it for a mere $20. And I don't mind matching, I'm not bringing a whole ton of dress-up clothes and my normal 'uniform' is a teeshirt and jeans, so the bag will fit in perfectly.
Whitewater