Clothing
Clothes seems to be the big think that people like to overpack. A wool sweater or jeans may be comfortable but cotton and wool tend to be heavy and take alot of space in your bag, I usualy like to go with synthetics. Synthetics sink wash easily, resist stain, dry quickly, and tend to be lighter, often you can also pack them tighter. Nylon zip convertable pants/shorts are appropriate for most casual and outdoor activities including swimming. My wife likes to pack synthetic skirts and either cotton or synthetic blouses wrinkle-free wash-and-wear is a must. Choose dark colored running/trail shoes these will be apropriate on the trail and if properly colored even on Shabbat. Tiva type sandles are heavy but if any swimming is in my plans as I dont like to rip up my feet on rocky river bottoms, flip-flops are suficient, usualy localy available, and lighter if you only want to avoid hostle shower foot fungas
I always pack a nice pair of pants (usualy synthetic black slacks) a white cotton shirt (although I have a synthetic silk shirt too) black socks, and a tie. Steam or a clean pot full of boiling water can both be used to de-wrinkle or iron your clothes for Shabbat. Throwing your clothes into the dryer with a damp towel will also remove wrinkles.
Shabbat
If you are not aquainted with a religious Jewish community you probably don't know about the best oasis to a weary Jewish traveler, Shabbat hospitality with a family in the place you are visiting. Call ahead and almost all observant communities will have a hospitality comitte check the ou.org website. Shabbat begins about an hour before dark know when it comes in. Showing up after Shabbat starts and not respecting the observance of Shabbat in the home of your host is bad form, be nice and enjoy the oppertunity to learn, if you are not sure of the customs ask.
  ¶ 7:35 PM