5 wt. Parachute Adams and flying ants have always worked well for me in mountain lakes. Heavily weighted wooly buggers or rabbit leaches are my go to wet flies.

If you are planning on doing more than a little fishing in mountain lakes I would suggest getting one of these...

http://www.campmor.com/outdoor/gear/Product___70062

Opens up a lot of opportunities. Doesn't take up much room in the pack or weigh too much.

Good luck.