To carry my gear around I have a Tamrac Expedition 5 photo backpack.
This is an excellent bag which takes my camera complete with long lense, a pair of binos, 3/4 spare lenses and all the other bits and pieces I carry around with me. The straps are wide enough to be comfortable

Zips on the bag are sturdy and the one on the main compartment has a weather cover which can be a bit of a pain in dry weather (when it's not needed) but does a great job of keeping the bag weather-tight.

Inside the bag are removable dividers which are almost standard in camera bags these days and as such work well. The front flap has clear plastic sections which I find useful for packing away any flat items such as lense covers, cloths or even my flash extender.

If I ever get round to buying a 500mm lense then I may go for a bigger version like the Expedition 7, though I'd only be tempted to fill it and then could I carry the weight?