As a general rule, any code you write on company time and on company resources belongs to the company.

But I think some common sense still applies. If you wrote some autohotkey or shell script that has nothing to do with the projects you worked on and boosts your productivity, sure, it’s fine to take it with you. For example, a script that pastes by typing the characters instead by pressing a certain combination of keys. Or a script that mounts the shared files drive in VMware.

But taking code from your company projects is not okay. Maybe you implemented some fancy new middle-out compression algorithm in your company’s product, and you would like to take it with you, don’t. Maybe that gives your company the competitive edge.

If you decide to build a competing product or work for a competing company, I would recommend being 100% clean. Read your contract carefully, and make sure you are 100% in the clear. Make sure that if your company wants to sue you, they have nothing on you. And maybe consult a lawyer.