Utility Cycling - best backpack for groceries (and everything else)

i'm looking at http://www.rei.com/product/778467 (mostly because i like the way it looks) for hauling a few days worth of groceries, or other quick errands
is 30 liters enough?
will carrying ground chicken, tomatoes, toothpaste, etc. on my back be a bad idea?
what can you recommend?


thanks!

Why not panniers? For summertime riding, you'll really appreciate not having a backpack on your back. Plus with a backpack (especially one that tall), the stuff on the bottom can get badly squished by everything else. YOu'd be amazed at the ability of your groceries to re-shuffle themselves in a backpack while you ride - the bread slides down next to the milk jug and gets mushed, the raw meat winds up on top of the fruit and leaks onto it, etc. With grocery bag panniers or baskets, it all pretty well stays where you put it, and you can separate your stuff into two bags based on fragility, raw meats, wet vs dry, etc.

For complete coverage of this issue, see this thread:
http://www.bikeforums.net/showthread.php?t=488170&highlight=grocery+bag (http://www.bikeforums.net/showthread.php?t=556662)

For what you've described as your needs, I'd recommend a setup like that of wahoonc, shown in post #9 of the thread. If you don't like permanently mounted baskets like his, you can always go with cloth panniers like those mentioned in this thread: http://www.bikeforums.net/showthread.php?t=556662

I don't like to carry anything on my body when I ride. I really like a rear carrier with Wald folding baskets. They are there when you need them and fold out of the way when you don't. If you use zipties to attach them they make no noise at all when they are empty.