Someone's MVC EF Project Won't Build - Things You Always Forget

Tools >Library Package Manager > Package Manager Settings.

Then check Allow NuGet to download missing packages during build.

Then rebuild the solution, and it should work.

BUT THIS WON'T WORK IF YOU HAVE AN OLD VERSION OF NUGET PACKAGE MANAGER!
Version 2.4 won't work, perhaps not even 2.6. Version 2.8 did seem to work.