If you have a freezer with excessive empty space, you can fill that space with gel packs, jugs of water, or even empty ​EPS coolers to help the unit retain its thermal mass during door openings. Just be sure not to load up your freezer with too many containers of water all at once!

To improve your freezer space, place your items in ziplock bags and freeze everything flat. This way, you can simply stack them on top of each other. Boxes are bulky, let's face it. If you shake a packaging box and you hear lots of rattling going on inside, this should tell you that there is plenty empty space inside.