Any good pilot or navigator has one, but neither Earhart or Noonan apparently discussed it or left a record of it with anyone we know of. It is said that Earhart, at some time when she was still back in the States, said that if she was unable to find Howland she could always turn back and land on a beach in the Gilbert Islands. In reality, that wouldn’t have worked because:

a. She wouldn’t have enough gas to get back to the Gilberts.
b. You can’t fly to a known destination from an unknown point.

You can, however, fly from an unknown point on a known line, along which are known to be several possible destinations.