I like to roll my daily "necessities" into a gallon ziplock bag - socks, underwear, t-shirt. You can then squeeze all the extra air out and keeps things watertight (because even if you have a waterproof bag you'll have to open it eventually!) and easy to pack/unpack (and see what you're grabbing!).
Especially handy because I usually just strap a regular old army dry bag on the back of my bike when I go - and there's absolutely no organization inside those things - or pack an assault pack (whose straps conveniently cinch down on my passenger grab bars) which isn't waterproof in the least. Either one can be packed for long trips as long as you aren't sleeping outside - and then I just toss my waterproof sleeping back on there too (once again, issued gear, stuff sack is easy to attach to bike or pack).