When I started off with my Canon 1000D Digital SLR (now replaced) back at Christmas 2009 I bought a small bag that carried the camera, spare battery and lens brush. The following Christmas I got the Canon EF-S 55-250mm lens which still fitted in the bag comfortably.
In 2011 I bought the Sigma 150-500mm lens (now replaced). For a while I carried this around in the box-like case it came with but this meant that I did not have a way of protecting/carrying it when it was on the camera. I therefore bought a big shoulder bag but I found that this was uncomfortable on long walks even though it had straps to carry it on my back.
I therefore spent a while looking at alternatives and finally bought a Lowepro Flipside 400 AW backpack.
I have been very pleased with this but it was a while before I realised that one of the reasons for the waist strap was to allow you to take the straps off your shoulder and swing the bag round to the front, open it and swap lenses etc. without having to take the bag off and put it down somewhere. It also opens at the back next to the straps so if you do put it down on muddy ground the part that goes against your back is still clean. With security in mind the only opening accessible to others is the pocket and not the main content section. With that in mind take care with what you store in the pocket if you are going anywhere where theft may be an issue.
For quite a while I was able to put all my kit in the backpack but now I have a few too many things and have to plan what to take,
The only downside I can think of is that the tripod fits to the front of the bag and the top strap tends to pull it against the bag and squash things up a bit. If the strap is not tight, or if I use only the middle strap then the tripod leans back and spoils the balance when walking. It might be better if the tripod was fitted to the side of the bag so that the weight is closer to your back. I have now started carrying the tripod on the side of the bag.
This filter is not normally fitted due to increased chance of “banding” on out-of-focus lines. Perhaps this is as a result of going for a cheap one. I may post about this sometime. I have noticed it on many wildlife photos on flickr and it is certainly not limited to this lens. The lens hood is deep enough to protect the lens from accidental touching. Maybe I will get the Sigma 86mm filter sometime.
LCD Display Wireless Remote
(mine is not on Amazon now but this looks like an update to it)
Nikon binoculars replaced with Opticron 8×40
I have occasioanlly squeezed my ASUS netbook in there too with a length of network cable and a pair of USB to CAT5 adapters that allow me to connect my camera to the netbook via USB but with the wire between them being readily available network cable. I have yet to use this in anger but it does work.