In the vein of all the previous posts, I also present my bag. I happen to also be an undergrad, but that doesn't mean my bag is packed similarly to the other two previously-shown bags. I like to bike everywhere, regardless of weather, and I do keep a few odd items on me.
In no particular order:
1. Surface Pro charger with micro-USB cable - it doubles as my phone charger, since MS stuck a USB port on the power brick.
2. Surface Pro 2. It replaced my physical notebooks. I still enjoy taking notes by hand, and the Wacom digitizer is a godsend in a world full of inaccurate capacitive touchscreens. It's also nice for drawing, since the pen has 1024 levels of pressure. I have Office 2013, VS2013, CS6 design premium, and IntelliJ installed, and the Surface Pro 2 gets the job done anywhere.
3. Canson 12x9 sketchbook. Sometimes a digitizer just doesn't cut it, and I enjoy the feeling of pencil on paper. I specifically use Canson, since their pages tear out to be a full 12x9 page. I also sticks papers in the sketchbook to keep them from being crumpled up.
4. Hand warmers. I started carrying these just because in winter. Never know when they'll come in useful, like walking 13 miles in sub-freezing weather.
5. Earbuds. For teh muzaks.
6. Mini-pump for putting air in the tires.
7. Cetaphil. I have really dry skin from taking Accutane in the past.
8. Tea bag. Why not? Sometimes I want tea.
9. TI Nspire CAS, for all my calculating needs. For most of my needs, it's surprisingly easier to use than Matlab or Mathematica.
10. Moleskine mini-notebook, for keeping notes and whatnot.
11. Mini multi-tool. Comes in handy. Sometimes I replace it with a bike tool.
12. Carabiner. Who knows when I'd need to use it? There's a second one of my water bottle. It helps keep the pack cover pulled all the way up.
13. Pack cover. For when it rains and I want to keep my backpack dry. I don't actually carry rain gear for my person, since I'm on a bike.
14. Assorted writing utensils. Includes pencils, gel pens, ink pens, and dry-erase markers. Also erasers.
15. Reflective band. It's useful at night - makes me more visible. Also, I can wrap it around my right pants at the ankle to prevent the pants leg from rubbing on the bike's chain and getting greasy.
16. Axe, for needing to smell good. Neosporin, for scrapes and whatnot. Benadryl for insect bites. Also bug repellent for not getting bug bits in the first place.
17. Sigg water bottle from years ago. It's been through a lot, but I'm attached to it.
18. TNF Heckler daypack. 34 liters of space - enough for books and whatnot during the week, and enough for the day trip on the weekends. It's lasted me 7 years now with only a bit of fading.
Not shown - I usually also carry a cliff bar in the backpack for when I get hungry, but I ate it.