My day pack is a National Geographic NG4475.
National Geographic Camera Bags & Backpacks | Manfrotto
It's a sling bag with 2 compartments and a map pocket at the rear.
Top (lightly padded) compartment holds Fuji X100 with lens hood, sometimes a small secondary camera, a ziploc bag with spare battery and filters, a phone, a steripen water filter, a flashlight, a roll of electrical tape and toilet paper.
The larger bottom compartment always holds some emergency medical equipment and medicine, and usually my 7" tablet plus keyboard, 900+ pages of lonely planet guidebook, tiny journal and French phrase book, pen, lighter, toothbrush and toothpaste. Sometimes I change its contents to hold sunscreen, some food, a solar charger or a lightweight wind jacket instead of some of the optional items.
A sling bag like this is great as a day pack for travelling. When I'm in an urban environment I keep it on my chest for security. The camera compartment is right on my chest so the camera is always easily available; also there's no way to snatch anything from it without putting a knife to my throat. When I'm hiking in a more rural environment, I usually put the bag on my back to reduce the strain (having it on the chest can get tiresome after a few hours, but then I do have some 3 kilos in there). If it's on my back, I can still easily slide it round so that the camera compartment is on my belly and I can take out the camera (would be nice if the zipper opened on the other end though, to minimize the risk of anything falling out). Switching from front to back is a matter of seconds. When I'm moving from one sleeping location to another, I wear my big backpack, and the daypack is on my chest meaning I still have everything important available without having to put down the backpack. I can attach stuff like a small sleeping bag or a water bottle to the side loops.
If you use it the way it was intended, it flops about more than I like (really stupid design, IMO), so I attached the lower end of the sling to the lowest of the side loops rather than to the flap underneath the sling. With the sling at its shortest length, that takes care of the flopping nicely. I might make myself a stabilizer strap some day, because if you have it on your back and you bend down, it sometimes slides away from your back and hangs off your side, which doesn't aid stability in the mountains... Other than that, it's very versatile and tough as nails, doesn't scream "camera bag!" and looks pretty cool if you ask me. I'm happy the previously white National Geographic logo has become dirty enough to not stand out anymore, because the questions of 'do you work for national geographic?!?!?' were getting kind of annoying.