You can borrow or rent bikes from your resort--we borrowed bikes (for free) from the Royal Mayan and biked the 3km to the ruins. We also took Ritz crackers to feed the iguanas, who will come very close to you if you come with crackers--any kind of crackers will do.
The ruins are small and really not much compared to larger scale ruins like Chichen Itza, Coba, Ek Balaam, or Tulum.