I'm looking for a do it all pack. I'm a big guy 6'3" 270. So size or concern isn't a huge. Though I don't want to look like I'm going on a 3 month backpacking trip. I'd like to stay around $150ish. I did get a $50 gift card to Amazon, so I'd also like to stay there too if possible. Primary needs are size with a laptop compartment and weather resistance and build quality. I have a 10mile commute in most times rain at 55mph on a Suzuki V-Strom.
If your school is in a gun free zone, I would check out bulletproof back packs and/or bulletproof clip boards.
Check out the Ortlieb Messenger Classic on Amazon: http://www.amazon.com/Ortlieb-Messenger-Bag-Classic-Silver/dp/B002DBNOTS/ Waterproof, tough as nails, doesn't have a lot of extra straps and buckles to flap in the wind. I can attest to their ability to keep stuff dry at speed. (Vstrom commuting in Seattle, WA) AND, at $140, well within your price range. (Their other bags are great too!)
Have you considered hard luggage? It'd be vastly superior for the mission you described, and you can easily get away with one of the Givi E36 or E45 for 130-140 bucks. The VStrom already has a great mounting surface right on the back. Waterproof, lockable, robust... Throw any old bag you want in the back, and you'll be set. That's my preferred setup for getting back and forth to campus, and it also allows me to lock all of my gear to the bike.
+1 for hard luggage. My school commute is about 1 hour there and 25 min back (damn traffic) occasionally in some shitty weather I always just wore my backpack under my rain gear if needed, but waterproof hard luggage made my trip at least 10x easier. Pull up on sidewalk under a pavilion, unpack everything, roll onto motorcycle lot, throw cover on, locked up and ready for class in about 5-10 min.
Kreiga makes superb gear, including 3 different sizes of backpacks, The gear is strong,totally waterproof, & beautifully designed. Pricing might be a problem. I don't know about the backpacks, but the other bags & such are premium priced & rarely if ever discounted. They are, however, well worth the price. The build quality is obvious & it's clear that the price is there in the workmanship.
+1000 on the hard luggage. I commute 30 minutes one way daily on my bike. I wore a backpack for a long time until I finally got smart and bought hard luggage. I don't know why I didn't do that WAY sooner. If you have your heart set on spending money on a special backpack for bike commuting, get a cheap halfway decent Jansport or similar backpack. No need to spend a fortune on a backpack. You don't need a special motorcycle one. If, however, you are really deadset on spending a lot of money on a backpack for commuting, get something waterproof. At least this way you can logically justify spending up to $150 :eek1 on a school backpack. Seriously though, do yourself a favor and get a top box. You'll love yourself (and us for recommending it) for it.
I have a Givi Hard case on the rear for securing my helmet and maybe my riding pants or my jacket if I really shove it in there. And thats a 52Liter model. I looked at a Klim Krew Pack. I certainly didn't feel that was worth the $135 it was asking for. It was small and certainly not suited for my purpose.
I commute 25 miles each way rain or shine. My bike is a Buell XB9SX which means no luggage. I use a Chrome Metropolis messenger bag and am very happy with it. Easier to access than a backpack since you can swing it around from your back to your stomach and pull things out without taking the whole bag off. It's big enough to hold a change of clothes, my big 15.6" work laptop, and a few other things. It could easily hold a long weekend's worth of clothes. When I'm sitting on the bike the bottom of the bag rests on the seat, so I'm not really carrying any of the weight on my shoulder. $160, made in America, built like a tank. There are about a thousand other companies that make bike messenger bags so it might be worth googling to see what else is out there. Timbuk2 is very popular, but mine isn't waterproof (the seams and stitching aren't taped so water eventually gets in) which is why I use a chrome bag now. The chrome bag is not waterproof in the sense that a drybag is, so I wouldn't go white water rafting with it, but I've never had anything inside get wet in upwards of an hour of moderately heavy rain.
Grab a helmet lock, and store the helmet on the outside. Should give you plenty of room on the inside for everything else. I'm able to fit my boots, gloves, jacket, and pants (both textile) inside of my E36. Helmet gets locked to the outside of the VFR. When I return to the bike, everything comes out, and the backpack goes in.
