Some of the examples from my next level layout talk given in Smashing Conf Oxford 2016
Technique combining flex-wrapping and css columns so that the component doesn't need media queries
How I progressively enhance from CSS Floats -> Flexbox - > CSS Grid
Technique for dealing with multiple items inside of a component
Technique for allowing you to have equal height columns
A simple technique for displaying a list in reverse to use on something like a twitter feed, comments, or an IRC Chat application
Demonstration of basic presentational source order shifting (Read about accessibility concerns: http://tink.uk/flexbox-the-keyboard-navigation-disconnect/). My recommendation is to only use this on presentational elements and things which won't be missed
Some of the interesting things I've come up against in using Flexbox with intrinsic sizing of iframes, SVG, and my workaround for responsive images.