When you receive a parcel, it often comes with bubblewrap or, better even, with those big 3x6" bubbles. Put them in the back of your fridge or freezer if there is space. It keeps the inside cool whenever you open the door. Result: lower electricity bill.
Though this may not work with newfangled always-on ones. I'm afraid we're a bit backward here and don't change our stuff unless they really conk out. And then we try to get second-hand.
If you can't use your bubblewrap this way, charity shops are usually grateful to receive it.