Yet another travel bag post... sorry

No need to apologize; the search for the perfect bag is a never ending one. But requiring the keyboard means that you'll need a bigger bag than you otherwise would carry, I think, because it introduces a bit of an awkwardly shaped and separate piece of equipment.

For a backpack, either the LowePro Photo Sport 200 or Photo Hatchback 22L ought to work. They're different kinds of backpacks - the Photo Sport is a bigger bag has the access hatch on the side for quick access. The Hatchback is a smaller bag, and has the access hatch on the side of the bag against your back. It's a more secure layout, but not necessarily the easiest for quick access. It's a smaller bag, too, but will have plenty of space for sundries.

Another backpack option is the Timbuk2 Sleuth. That ought to be plenty big for you needs.

For a messenger bag, my current go-to travel setup may work for you. I take an ordinary messenger bag (a Timbuk2 in my case), and use a Crumpler Haven medium camera insert. That way I have camera protection plus space for other stuff in a nondescript bag. I think a decent size messenger (say, equivalent to a Timbuk2 medium messenger bag) plus 2 small Havens (one for each camera) would do the trick for you.