Saving a variable from Chrome extension to be locally accessible

Question

I have a Chrome extension, and its popup.html has a <select> element.
I need its value to be saved into a variable, that can be accessible in the content.js.
I've tried to save it in the local storage but it does not work, also have tried sendMessage but can not get that to work, also checked multiple tutorials but no help so far.
Any suggestions? :)