Insulating windows during cold weather is a great way to use up leftover sheets of bubble wrap. You can use it to winterize cracks around your window frame, too. Here's how.
If you don't want to cover your windows in bubble wrap, or have especially bad cracks to seal, simply stuff the cracks with bubble wrap for insulation. Hold a strip of bubble wrap to the window frame centered on the crack. Push bubble wrap into the crack with a butter knife or other slim object.
Continue until the crack is filled with bubble wrap. Keep a corner of the bubble wrap sticking out of the crack enough so that you can easily remove the bubble wrap later with tweezers. You also want to leave a little gap at the top or bottom for air to flow in and out so that condensation doesn't build up over winter.