I support the idea of asking the coordinator! I also support the idea of light neutrals for Costa Rica. At first guess, I'd say a pair of white, cream, or khaki knit pants in a flattering cut (wide-leg or skinny), comfortable dressy flats or wedges (if you do a wide leg cut, make sure to hem them so the skim the floor when you're wearing whatever shoes). then I'd do some layers and include some bright colors. Keep it simple with just a pant, blouse and cardigan or jacket. You really can't go wrong.
ETA, I've personally had my eye on this white trouser, not sure if it would work for you (are you in the US? What size range do you need, and would the cut suit your frame?)
