In past few years, I’m using a light, waterproof pack I made. The trick to make it light and waterproof is to separate the load-bearing harness and a waterproof drybag. The latest, third version weights 320 grams (11 oz) and looks like this:

If you like it, you can find detailed instructions and patterns here: gear.rezacovi.cz/backpack_mk3/instructions.html
The website has some problems right now, you can also download the instructions here: http://rapidshare.com/files/175347142/instructions.zip.html

