Steel metal garbage cans. Unfortunately most people use plastic bins now. Get a steel metal can and lid. Line the interior with cardboard or other insulation and duct tape securely. Store a lot of electronics gear in it for when an EM burst hits. Make sure no metal is exposed inside to mess with the electronics gear. Make sure the metal lid makes good contact with the steel can. Connect a grounding wire to the outside of the can and ground it to a cold water pipe or other grounding connection. Your items are now protected and ready to use when the zombies roam.
If you have a metal shed you can improve its protective quality by making sure all the parts connect to each other to make a complete metal ‘shell’ and that it is grounded to the ground.
A wire mesh cage is enough to make a serviceable faraday cage, the more metal surrounding (but not touching) things in side, the better.
The electrical charge will go on the outside shell.