Here's a link to the ferry line:
They have a "reservations-only" policy (no standby travel) from Friday-Monday in the summer. But they'll take a reservation up to an hour before sailing time---book ASAP tho.
As far as camping goes, it's prohibited everywhere on public land on the island. There is one campground and it's close to where the ferry lands. Call Dan Feeney at MV Family Campgrounds, (508)693-3772 and see if he has any sites available before you make your ferry reservations.
Coop's and Larry's Tackle Shop can give you directions to some public access fishing spots around Oak Bluffs and Edgartown. You're going to run up against "resident-only" parking regs during the day in other places. There's also a public beach in the fishing village of Menemsha where you can walk a little to the right of the bathing beach and fish. Or you could fish from the jetty there.