One of the hardest things we had to figure out was what kind of shoes and clothes to take. The weather in Panama is the polar opposite of Utah. It's hot, humid and rainy, a ton of rain. Alyssa found a sister on Facebook who had just returned from Panama and she was a HUGE help in knowing what kinds of clothes to take and what not to. No cotton, it does not dry quickly and with the humidity, makes you constantly sweaty and wet.
Shirts and skirts - we bought mostly at Macy's (who will give you a 10% missionary discount if you tell them it's for a missionary, at least in Utah they will, not sure about elsewhere) and J.C. Penney's. She did find one skirt at Seagull Book and some at Kohl's online. 95% of what we bought are made out of polyester/lycra type blend so it will dry quickly. All very light weight. She did find a few shirts that are made out of moisture wicking material (think work out type clothes) that look dressier. She is taking a couple of things that are "dressier" for the MTC and zone conferences but most is casual dress.
Shoes - (see picture) The important thing here is "quick dry". We have been told the biggest problem the missionaries in Panama have is their feet so it is important to take care of them, which means you need to go for functionality not looks. We bought 3 pair of Keen type shoes. They are made out of a meshy type material and have rubberish soles so they will dry out very very quickly. She has one pair of flats and one pair of dressy shoes for the MTC and conferences. The other thing she got was 2 pair of crocs, yes crocs (apparently that is what all the Panamanians wear which goes back to functionality). Other than the Crocs, we got all her shoes at Macy's all on sale.
The last thing I would say is don't forget a pair of tennis shoes for p-days and flip flops for the shower (several people have mentioned to bring flip flops to us).