These ideas and techniques are the skills and ideas of Jen Leban. Check out her website for more!
You can use Google Draw or Google Slides to insert an image file, and then use the "curve" line tool to create an enclosed shape (filled in with green!) wherever you want to create a window for your face!
In this clip, I have a hallway in the school painted green (thanks, PTA!) specifically for green screen projects. I used green fabric to cover the floor, so that I would be surrounded by green, and then when I keyed the green out, I had a full standing figure that appeared to "float" wherever I placed it. I also shrunk down the top clip in order to exaggerate the size difference.
Pop-up green screen (check Amazon)
Tablecloths (check the dollar store)
Painted panels, like foamcore, plywood, styrofoam, or cardboard
Green fabric by the yard from the fabric store
Green bedsheet