Brian, there are beaches that will allow you on them with a jeep, including Westerly, Charlestown and Middletown. You need to get an access permit from RIDEM and the jeep has to have certain equipment in order for you to get the permit. From what I remember at a minimum you need an external (extra) gas can, a fire extinguisher, a shovel, etc. I'm not sure if a winch was also a requirement. Here is a link: http://www.crmc.ri.gov/offroadvehicles/BeachVehicleRegs.pdf.
Happy trails! Joe D