ICOM 706 MKIIG is as small as they get but with full feature operation, and an excellent DX travel or DXpedition rig.
Butternut HF9 VX is their 9band vertical that weighs less than 25 lbs. Get the stub radial kit for it, STR II and elevate the radials by attaching the insulated ends to your guy ropes and you'll be all set. Pelican makes a 50" hard case that the HF9VX fits into nicely. It has wheels and handles so you can wheel it through the airport and check it as luggage. pelican also makes smaller cases that will hold the ICOM. Yaesu FT 100D would be my second choice for a lightweight HF rig, but I've heard some models are having problems with a CW glitch.
If you want to take a Yagi, I'd suggest the Force 12 C3S tribander. You can go to Radio Shack and buy 3 sections of 5 foot TV antenna mast, cut them to 48" long with a hacksaw so they fit in your antenna case, then end feed the top and bottom sections into the center one with the tapered ends. You have to cut them so that the center one has no tapers and the other two have one tapered end each. This will give you a very portable mast and get the vertical up 12 feet.
Adam Boettiger, W7MPw7mp@dxpedition.com