Water shoes, I used them on two of the excursions
Swimsuit, I wished I had packed two as nothing seemed to dry in Panama.
Hat to keep your head from burning
Toiletries and Medical Supplies: Sunscreen is an absolute must for me in tropical climates, bug spray is another good item to pack if you are heading into the jungle
Miscellaneous: Credit/debit cards are not as widely used as they are in other places, bring US cash or an ATM card to get cash.
Although the balboa is the currency of Panama, it iso nly so by name. Do bring your US dollars here, Balboa banknotes do not exist. Often you will be told a price in Balboa - but what they mean is dollars. 50 balboa=50 USD.
The balboa is divided in 100 cents... and at least here you can find Panamanian balboas, as well as US cents. The Balvoa cents coins are interesting and bear the face of the Spanish explorer/conquistador Vasco Núñez de Balboa.
Clothing/Shoes/Weather Gear: Panama's climate is hot & tropical (@ 85-95 F) all year round. It also has frequent rains from March till November. Pack light and bring rain gear.