That really depends on the time of year, how long you are going for etc. You can find tons of packing lists on the web, but really think about what you want to take as, when you have to carry it, it really matters!
Remember, take as many pairs of socks as underwear as days you will will be doing laundry. If you take 7 pairs, that means you will have to do laundry every 7 days. Underwear is light, so take a couple extra pairs. Dirty jeans you can live with, dirty underwear - well, let's just say others may not want to live with you!