Do I need to use a comma with list items?
When we have a list of three or more items, we use a comma to split the items in the list. This comma is known as a listing comma, e.g. I like rice, beans, and plantains. Listing commas can usually be replaced by "and" or "or," e.g. I like rice and beans and plantains.
Listing commas can separate lists of nouns, verbs, adjectives, dependent clauses, or even complete sentences. This can mean that you can have a comma before an "and" that is followed by a dependent clause if it is the last item in a list of dependent clauses. Some authors like to join sentences with listing commas, e.g. I came in, I saw the package, and I opened it.
When using listing commas, the comma before the final "and" or "or" is optional depending on if you are using Oxford commas or not. How to use an Oxford (or serial) comma.