If you are using a backpack, I would put everything in the camera bag and put it in the pack on top where it is accessable. Fishmeister's idea for the plastic baggies is a good one. I've never had a problem shooting in the rain and both my camera and I have gotten soaked, but I wouldn't recommend my careless attitude to someone else.
I would take at least one (1) extra battery and at least one (1) extra memory card. If you can, figure out how many pictures you think you will take and plan on enough battery power and storage capacity for that.
I carry two lenses for the APCS cameras I use when backpacking. A 16-50 zoom and a 50-250mm zoom. That gives me wide angle for the panoramas and a reasonable effective 400mm for wildlife shots, etc.
If you don't have one, get a polarizing filter. They are great for landscapes. They take the glare off of leaves, giving you more saturation in the colors and when the sunlight is about 90 degrees to the side of what you are shooting you get really nice blue skies. If you are in an area where the rock formations are primarily granite and/or glacially polished a polarizer also cuts down the glare from the polished rock. This gives more detail in the rocks and because they reflect such large areas of light, help increase the contrast and saturation of the whole image. Large areas of reflecting rock (large in terms of area in the frame) don't create flare, but they will create a 'veiling' effect over the whole image.
Keep your most used lens on the camera for both convenience and because packing with a lens attached takes up the least room.
Hope that helps.
Vance