A good minor for engineering, in my opinion, is writing. May seem a little weird ;) but, I have found that strong engineers are ones that are able to effectively communicate. Good writing skills are a great way to effectively communicate. There is a perception that engineers are so technical that they just build stuff. So we do build stuff, but..if we can't effectively share what we have built then oftentimes we can't be as much help in solving a problem or creating something new.
To be clear a good writer doesn't have to be a person that writes many words. Many times, the shorter the better, which also means having a strong vocabulary and knowing how/where to find words that matter. A good writer, particularly in technical fields, doesn't write with too much "fluff" but can quickly convey meaning in a way that is easy for others to understand, even if the work and energy that was put into their creation was really hard.
I hope you find this information helpful. Best of luck to you!