Interesting to see this thread. For over almost 15 years I've required nothing more than a broadhead file sold by Kustom King. I taught myself the technique to get a blade 95% sharp using the file sides, followed by another 3% using the file edges as a steel. The remaining 2% sharp I don't care about honestly, but I have on occasion used cardboard, leather and Masonite as a final strop.
As for glass, you don't need a car window. A tumbler, drinking glass or ceramic coffee mug rim works perfectly fine as long as it has a radius. The trick is to start light and go lighter on pressure until you are almost not even touching the rim on the last 2 alternating strokes. All this work is doing is aligning the fine finished bead or edge and trueing it. Done correctly it's a good adjunct to final finishing and razor-quality sharpness.