Be sure to bring plenty of warm clothing and a good tent if you camp out. It can get quite cold and drizzly even in the dry season.
It’s possible to camp in Parque Nacional Volcán Barú , which you may want to do if you hike to the summit . The fee is US$5, but good luck finding someone to pay it to. If you want to do things by the book you can buy a permit ahead of time at the ANAM office in David  or Panama City .