Take the bus from Gamboa to Albrook Bus Station. From Albrook, go to the Bocas del Toro counter and purchase the ticket to Bocas. The price is $34. The busses leave at 6, 6:30 and 7 and be there 30 minutes before the bus leaves. Bring a blanket since the busses run the air at full blast. The ride is 11 hours. OR take the bus to Albrook Bus station, take taxi to the Albrook airport and take the 45 minute Air Panama flight, tickets are about $260 round trip.
If you are coming for a quick weekend, go with Air Panama. Otherwise, use the bus.