I have used a std backpack in the past, they keep banging into each other. And when you pull the camera out the lens cap may fall off ..
I use a Lowepro Photo Runner which is a shoulder and a belt bag. I use that I when I am overseas and when I go for other other regular stuff (not specifically photography). It can carry a SLR and 3 lenses - not pro 2.8s though. Nikon D70, 12-24, 18-200 or a 18-70 and maybe a fast 35/1.8 for example. For film, Nikon F100, 18-35, 80-200 and maybe a 50/1.8 or a 85/1.8. Doesn't carry a water bottle. It does have a zip pocket for a not too large guidebook but when I travel I have photocopied pages anyway. It has 2 buckle clips which you can do a make shift tripod holder. I use a compact one that folds down to about 30cm. It is a Gitzo traveler. 1550T I think. The new one now has a AW cover too.
At home I use a Lowepro Primus AW backpack. It has a top compartment for other stuff and a side bottle carrier, a tripod hook at the back. Lower compartment I can fit a body + a pro 70-200, 2 other lenses. One of them probably a 2.8 24-70 but I don't have one. If no 70-200 pro lens you could fit an extra lens there too or a flash unit etc. I don't really use the tripod hook, rather hand carry it. The lower compartment on this and many other backpacks have the zip on the inside. So you have to take it off before you can access it.
I don't really take that much items out so I try to get no more bags than I really need and keep the physical size down too and the money down.