First of all... I gotta ask this... you're doing 2-3 days in 3 different NPs? Are you actually backpacking or just camping. I have spent a whole solid week in Kings Canyon alone, and didn't even scratch the surface of that place - and we only went through Sequoia out of necessity because the road forces you to. If you have 3 days, you can barely do Yosemite as it is, much less the other two...
Anyways...
Shoot 35mm film. Digital is a fucking pain in the ass when backpacking, and it weighs a ton. Film weighs way less than batteries, and unless you're doing timelapses film really is the way to go (I mean, if it was good enough for Ansel Adams and Co....)
That said. If you must shoot digital, at least you're only doing 2-3 days. I get about 3 or so days out of a BP-511 on my 20D, and got about the same when I had my 5D. Unless you're shooting timelapses, you might be alright, depending on your camera, it's power efficiency, and the mAh of your batteries...
Regardless, I'd turn the brightness on your screen to the lowest feasible level, and conserve the shit out of them. Put it on like 30 second auto turn-off. Make it so you don't have auto-review, either.
For a tripod, either buy one of those really light, plastic, cheap tripods, a gorilla pod, or hope for the best. Lugging around a weighty tripod sucks dick, even with the most well supported bags. If it breaks out there, then whatever, do what you can. weigh it down using your pack if you need to.
Keep your camera gear close to you, and available as possible. I keep mine in the hood of my pack, or around my neck, almost at all times.
Bring only two lenses, or a wide standard, like a 35mm equivalent. I spent 5 days backpacking in the Trinity Alps with just a 28mm, 4 rolls of film, and my lightest film SLR. I shot about 30 exposures a day, and still had about 12 un-exposed shots remaining when we got back to the trailhead. In some cases, I would have really liked a longer focal length, as 28 is too wide for most wildlife.
If you're going digital, I'd recommend doing something about the same - especially in those three areas, which tend to be extremely rugged. I'm not sure if you're trying to capture any wildlife, but if that really is a thing you must do, then decide whether it's worth taking a long lens with you on the trek here and now, because if you're not using it, you're wasting it.
