Here's what I am using.
Single shoulder backpack designed to maximize utility when rotated towards front of body. Fits up to 15.4" (diagonal screen size) laptop computer. Plenty of room for my IPad in its' Otterbox Defender case, Apple keyboard,cables, and IMP880 ultra Pack 8900mAh Charger, soon to be (IMP1000, (11000mAh capacity) Extreme Pack for iPad) (shipping Nov 6 they say).
BTW, I also have a:
METHUSELAH Gear Bag Medium padded gear bag with sleeve to hold a 13.3" or smaller laptop computer, in case I want a more conventional look (like a small briefcase).
Both are very rugged and built to last forever....
FWIW, thought I'd ad what I'm using for more options.