I must have 5 or 6 day packs and the only "name brand" one is a Golite "Day", which I actually use as a 2-3 day pack.

My very favorite "day" pack is a lightened (cut all the useless bling off it) book bag from Walmart. If you have kids, you probably already have one somewhere...mine is recycled from my kids school days. It's been all over the world with me. I think it has a Jansport label on it.
It's my main motorcycle back pack too, since it will bungee on my luggage rack without hanging over the sides. Use it in the kayak too.
Another favorite is a flimsy little pack that rolls up very small, I picked up somewhere like Old Navy. Not as robust as the book bag but very handy.

Don't get caught up with name brand "backpacking gear" packs. Surf your local discount store and use your imagination. I don't like dedicated hydration packs, and prefer platypus's with a drink tube...then, any pack can be a hydration pack.