Well, I like the clothes-in-the-zip-lock trick because it lets me segregate things: T-shirts in one, underwear in another, socks in a third, and so on. So I can use differently sized bags for different batches of stuff, depending on what Im storing.
But certainly, compression sacks make a lot of sense, particularly if you can squeeze everything into one sack. And Sea to Summits compression bags (seatosummit.com) probably are the best ones out there right now. They have bottom panels made from eVent, a waterproof-breathable fabric also found in a handful of outdoor jackets (such as those from Integral Designs; integraldesigns.com). Because eVent is air-permeable, a bag made from it doesnt need a valvethe fabric itself lets the air out, the compression straps hold it all in place. The bulk of the bag is made from a polyurethane-coated material for maximum waterproofness. Theyre moderately expensive bags, but not too bad$30 gets you an 8X18" bag with 854 cubic inches of capacity.
As for the Ursack, nothing else out there is quite like it. Some readers will know that the Ursack ($65 for a 650-cubic-inch bag; ursack.com) is a bear-resistant food bag designed to replace bulky, difficult-to-carry hard containers. Its made from a super-tough material that bears find nearly impossible to penetrate. The idea is that you put your food in the Ursack and tie it to a tree, ten bears cant haul it off. The bear can, of course, crush the hell out of the food inside the sack, so for that reason the Ursack people now offer an optional aluminum liner. And it is highly recommended that food is first placed inside a waterproof, odor-proof liner bag. The Ursack has gained some acceptance among the bear-handling community, and it seems like a good alternative to containers like the Garcia hard container ($70; rei.com).