When I travel for leisure, I take a Canon 10D DSLR, along with a Sony VX2000 prosumer camcorder. I have a Lowepro Minitrekker backpack which nicely holds both cameras, three lenses for the 10D, chargers, tape for the camcorder, batteries for both cameras, and a whole bunch of extra support gear. It even has room in it for my laptop (though that becomes a very tight fit), and fits nicely under the seat in front of me. It's padded in the right places and offers great protection.

At my destination, extraneous gear stays in the hotel, and the backpack goes with me and my cameras, and has room for a sweater, small purchases, a folding umbrella, etc. The backpack itself is rain-proof.