Travel Preparation for Costa Rica

So, packing for 7 days in Costa Rica has become half the fun of getting ready for the trip. I am trying to limit myself and have one bag (a rolling carry-one) plus my backpack for the trip. Every item I'm packing has to do at least 2-3 things- and YES I am already packing!
Forget normal shampoo & condition- I went to REI & found these great little "sheets" of soap that are 1x2 inches in size- talk about light packing! And to top it off, there are 30 in the little packet- I hope I don't have to wash my hair that many times.
I bought the "large ziplock" packing bags that you put your clothes in and remove all the air- 5 shirts (2 long sleeve & 3 short sleeve, for layering) take up less space than 1 normally packed shirts.
I found the perfect backpack- which has built in pockets on the waist to hold my camera, phone, and video player- so that they are never in the back and out of reach! It even can hold a water bladder if I want to use it-some new inventions are just great.
I'll update as I increase my "packing" and will get a couple pictures out for everyone to see how I'm doing- pass on your helpful hints too!