On my critical list are water, waterproof hat, wool gloves, spare socks, ultralight space blanket, fire starting stuff (candle, bic lighter, waterproof matches), light rope/cord, string, lightweight poncho, watch cap, first aid kit, swiss army knife, paper (both kinds) and pencil, compass, candy bars, spare bow string, and maglight w/extra bulb and batteries. Also good to have are a light sweater, sandwich, 2-way radio that uses same batteries as light, mirror, and a double handful of rocks to slow me down. I'm sure I left something out.
I've gone out under beautiful conditions and been rained, snowed, and iced on before getting back to camp. I've been caught in a thunderstorm when there was lightning below me! Truly scary. Take no chances in the mountains- you can't see it coming from behind the mountain, so the weather can change in a heartbeat and kill you, or at least make you damned miserable, if you're not prepared. If you kill that beast way out there, you may be caught out after dark or have to stay over, too. When I killed my first elk, I got back to camp at midnight, exhausted and very happy!