Yes, they're Camelbacks, yes they're good at growing fungus, but yes the Army is really big on equipment maintenance, so it's not a big deal. Believe me, having to fumble with your stupid canteen -- getting it out of the pouch, undoing the tether you attach to keep from losing it, unscewing it, taking a drink, then getting it back in that awkward pouch is a huge pain in the arse. Keeping a Camelback clean is definitely less work.
Soldiers are explicitly trained to keep their fingers exactly as you see 'em in the picture. Less chance of an "accidental discharge" (yes, that's what they call it!) if things get tense, plus it's just as obvious to the civvies that you aren't about to shoot them. If it were a movie still, the fingers would be <I>in</I> the trigger well, where they don't belong.
That guy in the middle sure looks like he's pointing his rifle at the little kid, which is a big no-no. He was probably in the middle of turning around and the picture snapped at just the right time.
And again, if it were a movie still, you can be sure their uniforms <I>would</I> match. The fact that they don't probably has more to do with the haste with which they were brought to the country. I was just surprised that the 82nd Airborne wouldn't have all that stuff ready, just in case. Or maybe they're just short on funds like everyone else!