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 [1], which you may want to do if you hike to the summit [2]. 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 [3] or Panama City [4].
Links:
[1] http://www.moon.com/destinations/panama/western-highlands/volcan/sights/parque-nacional-volcan-baru
[2] http://www.moon.com/destinations/panama/western-highlands/volcan/recreation/hiking
[3] http://www.moon.com/destinations/panama/western-highlands/david
[4] http://www.moon.com/destinations/panama/panama-city