You may want to consider two of the large mountainsmith lumbar packs (mountainsmith stuff in my experience is very high quality/good value). The two lumbar/butt packs are the "day" and the smaller "tour".

http://mountainsmith.com/products.asp?subCategoryId=3&categoryId=4

You can get them cheaper then price listed on their site - I got both of them on ebay a few years ago. The bigger one is the "day" and it holds ovver 850 cubic inches.

For REALLY high value in a day pack, get the $40 LLBean "classic continental rucksack". One big compartment, three side pockets, everything excellent quality. Holds 2000 cubic inches. Very versatile - I love mine. Just a great bargain with many uses.

Reviews on the LLBean website.

http://www.llbean.com/webapp/wcs/stores/...8-sub2&np=Y