Surprisingly, there is storage at EWR (JFK as well).

Remember running into it once while waiting for bags...was hoping they could deliver my golf bags to my home so I could take the train as this is the service CO uses when luggage is delayed. That feature is expensive, however luggage storage at EWR itself is actually reasonable from the Trip Advisor post pasted below:

The company is called NBS Storage and Delivery and they have a desk at Carousel #1 Arrivals level, at Newark International Airport. They don't have a web site, so if you need additional information, call them at (908) 933-0503. They open at 7am and close at 1am.
They stored our luggage, 2 bags in total, while we went into Manhattan for the day, before our flight. The total cost was 15.00.


**But if you want to walk to the Marriott I'll bet you can get away with a smaller tip.