Never Buy Envelopes Again?

Some time back I found myself in need of an envelope. I looked all over the house and there were none in the whole place. I’d have to wait until I went into work and find one there. Then it occurred to me I had a printer filled with paper! I made an envelope out of printer paper and posted the items I needed to deliver. There is probably some moral there about thinking in terms of labels rather than seeing actual form and function. An envelope is just folded and fastened paper.
This incident got me interested in if there were better ways to construct envelopes. Given that Christmas is coming, this seems a good topic to place on the blog today.
Below is a pair of videos on making envelopes. There are many alternate ways of doing this, as you will discover on youtube. These  two are origami methods that are useful if you need something more decorative. This page on the Art of Manliness site shows a simple variation that produces an envelope that stays closed.