BubbleWrap insulation: Use bubble wrap on windows for two three+ years now, and I'm amazed how quick and easy it is. This year, we are even covering the windows in the guest room -- we just take the bubble wrap down when guests come, and put it back up when they leave -- 15 seconds a window.
Resealable (Cat Proof) Magnetic Window Insulation Tutorial
Love this idea for a headboard...If you use this idea make sure to completely remove all the glass panes! You don't want to end up in the ER if you accidentally hit your head on the glass during the night!