Neuroscientist here.

Being in SAS, I believe you could only get minor or certificate in CGS, and that wouldn't likely do much for you.

Neuroscience is a research field, and you want to put whatever extra academic time that you have into getting into a research lab and obtaining as much research experience you can. Find a lab whose research you like, with people that you enjoy being around, and work your way into a research project with a goal of having some authorship(s) on a publication(s) by the time you leave Pitt. That will do more for your grad school, med school, or any other science aspirations than anything else.

If you want to pick up a dual major, you could for something in biology (like cell biology or biochem) that could complement the instruction you'd get from the neuroscience department but for which you'd have decent overlap in prerequisites. If you are interested in computers, modeling, or stats, think about those areas because computational neuroscience and bioinformatics are booming areas. Or look at a certificate in the History and Philosophy of Science, because Pitt's program in that is literally #1 in the world.

Keep in mind that admission committees are often more impressed by dual/double majors that indicate a breadth of learning, something perhaps outside of science. But the number one thing (other than having to have the standard good grades and good GRE/MCAT scores) that will set you apart from the crowd is having undertaken significant research experience with publications and presentations to show for it, which helps demonstrate that you understand and actively took part in it, not just followed protocols for lab tasks without really getting the bigger picture.