Messenger bag recommendations? 1x dslr w/lens attached, 1x lens, 1x flash?

Any recommendations for a shoulder bag (messenger-type) that's small but can fit:

1x pro-size dslr (Nikon D750 with battery grip) with an attached medium sized zoom
1x extra medium sized zoom
1x flash

And a pocket to fit documents.

I've been looking at the ThinkTank Retrospective 7 http://www.bhphotovideo.com/...r_Bag.html but it's expensive.

Think Tank has some of the best designs in messenger bags. I don't own a messenger bag, but they'd be on the top of my list if I was to need one.'

Do a search on YouTube for messenger bags; there should be plenty of reviews.