I dunno, Liz. I guess they havent yet taught you the art of compromise in grad school. You know, where you give up one thing to gain another.
Same for packs. You want a book pack. And a hiking pack. And a hydration pack. But a book pack is kind of a casual fashion thing. A daypack for hiking is something else. And a hydration pack is a third thing. And kind of a useless thing, really. I mean, I occasionally use a hydration bladder on a bike. But otherwise: really? A water bottle doesnt work?? I cant get my head around that.
Anyway. Your first pick ought to be REIs Novara Commuter Backpack ($70). Its ideally suited for your biking world, and an easily hold a laptop, books, and doggie things. Its designed to carry well on a bike. And it will be OK on a trail. Not a ton of room inside itonly 1,500 cubic inchesbut itll hold clothes, a snack, and water. And it will adapt for a water bladder if that is what you really want.
On the more backpack-y side of things, there is the Osprey Stratos 24 ($99). Same size as the REI pack, but a little less streamlined as its mean to be carried while walking. But you can use it on a bike. Itll take a hydration bladder, it carries great, and its design gives you easy access to the stuff you need.
Lastly, Gregorys Z35 ($139) goes all the way in the backpack direction. Bigger than either the REI or Osprey packs (2,500 cubic inches), it is a bit of a lump to carry as a bike pack. But it will do on a bike, and otherwise its an excellent all-around daypack.
So there you go. One of these ought to see you through grad schooland years beyond.