From personal experience / use I can recommend the Kelty MAP 3500, available from Amron International for $89 or $99 http://www.amronintl.com/products.cfm?root=92&sub=&catID=93&Ind=ALL&pageID=159 The 3500 is good for my 3 days, ymmv you might find it small depending on what you consider a 3 day load. It has proven to be an excellent pack over the past few years, I also use it as an almost every day daypack it hauls overnight and extended day provisions very well. I notice that its available now in 3 colors - ACU, black and foliage green, too bad my favorite was coyote brown. I imagine it would carry aboard airlines quite well. I own three - and I get no $ from Kelty or Amron for the recommendation, just a happy camper.

There are several other military style packs described and depicted in this thread - http://www.ar15.com/lite/topic.html?b=6&f=10&t=186483&page=1. Amron also sells other designs too, have a look there.