Unemployment benefits. We talked to the unemployment insurance offices in New York and Massachusetts. In both states, you can continue to collect unemployment benefits while externing or interning (assuming it's unpaid) because that counts toward the mandatory provision that you are actively looking for work.
However, it's important that there is no promise of a job at the end of the externship because that would turn your externship into a trainee or temp position, and trainees and temps must be paid and can't collect unemployment at the same time. Rules vary nationwide, so check directly with your state before assuming the laws in your area.