Many Ocean City Campgrounds. One of the most popular is Frontier Town
www.frontiertown.com A lot of people take their bikes there to travel from the campsite to the pool and other rec areas in the park. Other camprounds include Treasure Beach in Delaware
http://www.treasurebeachrvpark.com/which is just a couple of miles outside OC MD off route 54 and Castawya Park
http://www.castawaysrvoc.com/. I don't know much about that park. A little further away off route 50 is Fort Whaley
http://www.fortwhaley.com/
There are many bike rental places on the boardwalk. Too many to mention and since I have never rented one in OC, the best thing to do is to go to
www.google.com and type in Ocean City MD bike rentals and a whole slew of them will pop up.