I still carry around much of my life in two bags that are always packed for just these types of situations, so I might grab them first of all (the picture also includes what I have in my pockets, and is a little outdated in that I don't carry the binder, that book, or that polo shirt any longer, but have replaced them with an outdoors survival guide, a pair of earbuds, a padfolio, a USB cable, another thumb drive (4GB), a different polo, and have my Lenovo X61 tablet with power adapter in there now instead of the MBP):

Contents:
1: A couple bluebooks.
2: Binder with a copy of my advisement materials and a hardcopy of the due/test/important dates occuring in a semester along with a small calendar
3: Garbage bag and plastic grocery bag
4: My trusty Jansport Odyssey 38 backpack
5: Notecard with various paperclips clipped to it
6: Extra pencil lead and staples
7: Extra thick latex exam gloves
8: Travel umbrella
9: Light but sturdy weatherproof jacket with basic jersey gloves with grippy dots in pockets
10: Roll of toilet paper
11: Pill container with various pain killers and my prescription meds, stuffed with cotton balls so that it doesn't rattle
12: Piece of paper containing ethics terms (not important)
13: Mechanical pencils. One for notes, one for tests, one for backup, one for lending out to people
14: Pens. Good pen, Sharpie, erasable pen, felt-tip pen
15: Various highlighters
16: Pens for lending out
17: Pouch containing dry-erase markers and a piece of chalk. Brownie points if you can lend a prof stuff to lecture with
18: DVI to VGA adaptor
19: AAA Mini Maglight with clip
20: Notepad
21: Wilson small gym bag
22: Three packs Orbit Bubblemint gum
23: Microfiber polishing cloth for glasses
24: Small staple gun
25: Compact stapler
26: Inhaler and Cold-Eeze
27: Condom
28: Altoids box
29: Kleenex
30: Toothbrush
31: Copy of photographers' rights article and NM trespassing laws
32: Keys
33: Antiseptic wipes
34: Band-aids
35: Nissan stainless steel thermos
36: TI-89 graphing calculator
37: Two packages Nature Valley granola bars (not pictured)
38: Pocket comb
39: Two wallets
40: MacBook Pro (power cord not pictured)
41: 1gb thumb drive
42: Book (misc)
43: LG AX8600 cellular phone
44: Swiss Army knife
45: Zebra pocket pen
46: Lighter
47: Chapstik
48: Clothing roll containing clean polo shirt, underwear, and socks
49: Battery powered alarm clock/radio/sound soother
50: Hat (not pictured)
I also have a Halliburton Zero case loaded with cash, a gun with a couple boxes of ammo, a bullet proof vest, a proper jacket, and spaces for my MBP and my SLR.
However, all of that said, depending on the situation I might not grab the Wilson bag or the Zero case. Losing the Wilson bag loses me my change of clothing, a book, my alarm clock, and the toilet paper. As I typically don't have the MBP or my camera in the Zero case, and the rules don't say that I can quickly load them, I'd probably not pick that up either.
Thus, my three items would be my backpack, MBP, and my favorite childhood stuffed animal. How's that for a combo.
In reality, backpack, Zero case with camera and MBP, Wilson bag with stuffed animal and whatever extra clothes that are handy tossed in, another camera around my neck, headphones on head, grabbing another jacket or something else as I walk out the door. Absolutely reasonable in three minutes if I'm already dressed as I have all of it lined up and ready for exactly such a thing coming to pass.
-Pufer