I have the same camera as Bryan. This year I bought a new Lowe toploader which has a better rain cover.
I carry only one lens and make sure it is relatively light. The case is carried bandolier style over my shoulder. With filters and a spare battery this comes to just over 2 kilograms which I think is worth it if you are really inot your photography. To some extent the weight on your front helps balance the weigt of your pack.
This year I caried a tripod bringing the whole load up to 3.5 kilograms. Perhaps, this is no advisable.
The weather was so bad this year that I hardly used it all!