I usually use my Timbuk2 bag:
Like how it has all the pockets for keys, tablets (can fit my Prime in there easily as well), phone, groceries. It's comfy when it's empty but can fit a ton of stuff in them as well.
Saw a messenger bag on The Verge that looked gorgeous....until I found out it's a small fortune to own. An Ernest Alexander bag:
They go for about $300+.