What is your favorite brand and size of daypack. Do you prefer less weight or more structure. How about water resistance. Vote for your favorite.
should be comfortable regardless - and water proof is a plus. I like the NorthFace daypacks - but some may think its too much for urban travel. The RS one is ok but i like a bit more rugged design and good features that do well in both hiking- or urban- day trips!
After trying out many, I've come to love my Eagle Creek bag (Daily Shoulder Bag).
http://www.eaglecreek.com/bags_luggage/shoulder_bags/Daily-60165/
Not too big, not too small and easy to keep close to you and in front in crowded areas. I think I paid around $25 through a Swiss Luggage website...I just googled it and searched for the lowest price.
Oh, in terms of water resistance. I recently stood in a downpour during an 8-hour D-day battlefields tour and everything inside was dry. I was amazed!
Lands end also had a small hideaway pack for 12$ or so. It was similar to the RS Day pack in size - but folded up into itself in a pocket. It also had a little bit more robust material in the padded straps than most "hide-away" day packs. But go try out a few to find out what you like. A super flimsy one with heavy items will soon be uncomfortable as its not made for a heavy load - so proper padded shoulders may well be worth $45.