I have a variety of different camera bags, backpacks and so on (I have the Slingshot 300AW).
What I have found works best for airplane travel if you're not willing to check a locked Pelican case, is a medium sized Eagle Creek cargo duffle bag, into which I can fit my Sligshot 300AW loaded with anything that can fit, and also a Lowepro Toploader AW 75 (the longest camera case they sell), AND a manfrotto 3051 3-section tripod (nowadays something lighter and a little smaller), plus a number of other things (like a ballhead removed from the top of the tripod).
The camera cases keep things padded, or I can also pad out a few other extra lenses with clothes (Galen Rowell recommended this travel technique even when checking lenses and cameras!!).
The best part about a duffel bag is it looks inconspicuous, it doesn't seem like you have a lot of gear - but even better no-one questions its size to fit in overhead storage. In particular I mentioned it was an Eagle Creek bag because that particular bag has been very strong, and has not had any issues with wear carrying all this gear.
And because you get a personal item in addition to the duffel, you can have a whole separate laptop case - I have a a pretty big bag that I can fit a 17" laptop in, along with a ton of accessories and a few books and a compact external HD (really two, one for backup), as long as it looks like it will go under a seat you are fine. On a regional commuter jet I remove the slingshot and Toploader case from the duffel to carry them on-board with my laptop (they can fit in the smaller overheads) and hand-check the duffle bag (this is the time where whatever is left need to have decent padding).
The downside of this whole system is: no wheels, you'll have to carry everything you can put into it. That's why you should not get anything larger than the medium sized bag...
But again, to re-iterate - the upside is you don't look like you have a ton of photo gear and you'll never have anyone say "that's too big to bring on board".
Now that's just for air travel, you also mentioned you'd like extra space to carry a guidebook and a few extra things while on location. You could get the 300AW, that might have enough space for a guidebook too. Or you could get the long toploader case, a lot of books would fit in the side compartment and you can carry a camera with a lens, plus and extra lens under it if both lenses are not too long. Or just get an iPod touch and use guidebooks from that.