One note about the space blanket - I had to use one my first hike on whitney (it was 9* at the summit at sunrise, we had to wait about an hour to get warm enough to hike back down) They are really hard to control and get wrapped around you. I HIGHLY recommend investing the 10-15 bucks and getting this:
http://www.rei.com/product/813511/sol-emergency-bivvy.
It's only 4 oz and comes all tightly wrapped up in a little bag a bit smaller than the size of your fist. It's a slightly heavier material and sleeping bag style, so you can easily get it around you and get your whole body reflecting heat within it (rather than just a flimsy mylar sheet that doesn't want to stay put).
