I personally use a Lowepro Mini Trekker AW.

It will easily accommodate the gear you have in mind, although you didn't specify what lenses other than the 100-400 you'll want to carry concurrently. If it's something big, your options suitably diminish.

I've flown (domestically) with mine, loaded with camera, 300/2.8, 70-200/2.8 and 16-35, plus other odds and ends. It won't hold a bottle of water with that gear, but the bag does have provisions on the outside for attaching a tripod (I place my tripod in my checked luggage and never carry it on my backpack).

Being a Lowepro, it does look like a camera bag, but even if the bag doesn't look like a camera bag, the tripod attached to it might tip off unsuspecting observers...

Edit: The Mini Trekker AW also has loops for attaching Lowepro lens cases, which can be handy for holding drink bottles.

PS: Check out this video to see how much the Mini Trekker AW actually can hold: http://www.mackstyle.net/minitrekker.mov