There\'s a number of keyboard shortcuts and menu commands to automatically expand or collapse all foldables in the current document. Ctrl+M, Ctrl
I know this is an old question, but here's an update for visual studio 2019:
The Quick Tasks solution from @ygoe's answer does not work for Visual Studio 2019, because that version changed the way the Quick Task bar searches. Plus it was never the preferred solution to the original question, since you needed to type a quick action instead of having a keyboard shortcut.
I found a different solution on the marketplace which does exactly the collapsing and expanding of all regions in the currently opened file with keyboard shortcuts: Collapse Region
From the extension page:
Default key bindings are (Ctrl+R, Ctrl+Num+) and (Ctrl+R, Ctrl+Num-). Can be changed in Tools->Options->Environment->Keyboard.