I usually use fewer batteries than I expect to. When I shot a 5D (with the PB 511 batteries) I would carry as many as four batteries – but I rarely if ever went through more than two, even on some quite long trips. That said, I’d rather carry the weight of an extra battery I don’t need than end up unable to shoot! Two things can increase battery use for me. First, I sometimes do some night photography in the back-country, and the long exposures eat up battery power very quickly. Second, I like to use the live view mode on my 5D2 for manual focus for many landscape shots – but this also creates a tremendous battery drain. It is easy to go through a battery in half or even a third as many shots with live view.

During most of the season water is rarely a problem – it would be rare to go more than a mile without seeing a lake, a creek, or a small rivulet. Later in the season some water sources can dry up in the Sierra, so it is a good idea to check local conditions at that point. (For example, Rafferty Creek, along a popular trail to the Vogelsang High Sierra camp in the Yosemite high country , often goes completely dry late in the season.) A filter is standard equipment these days.

The lens or lenses you’ll want, as you point out, depend a lot on your own personal preferences and what compromises you are willing to make – and how much weight you will carry. If I’m traveling very light I might use only a 24-105 on my full frame DSLR, along with a tripod and so forth. More likely I’ll also have the 17-40 along. On shorter trips and those where I want a bit more reach I add the 70-200mm f/4 lens.

Dan