For me, one of the most useful extensions for Visual Studio is Charles Bates' Document Auto Save. It simply saves all modified documents when Visual Studio loses focus. This is brilliant if you use git outside of Visual Studio as it means git gui always shows your changes when you rescan.
For some reason, Charles hasn't put the extension in the Visual Studio gallery, so it's slightly more convoluted to install, and probably doesn't reach as wide an audience as I think it should.
Read about it here or install it using the instructions on this page: