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.
Novara Commuter Backpack
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.