Does this come with the actual fish tape cartridges or do you have to buy those separately?

No, this is just the base unit which is a motor essentially. Milwaukee 2873-20 does not include a fish tape drum, battery or charger. You would need to purchase a fish tape drum separately, or opt for one of the kits which includes the drum as well as battery and charger. All options can be found at the link below.https://www.toolnut.com/catalogsearch/result/?q=m18+angler