Luggage and bags:
A backpack that suits you. Don't choose one bigger because you MUST bring that extra t-shirt. Choose one with the proper size and padding for a constant up-hill hike. Yes, it's a HIKE not a WALK!
Clothing/Shoes/Weather Gear: Bring something for wet weather - a cheap poncho made of plastic is fine, but bring two in case one rips. Forget about a raincoat...you'll pass out from the humidity.
Have good hiking boots, or very solid sneakers (American/European tourists tended to have boots; Costa Rican tourists climbed up in sneakers.
Bring something WARM! I bought a cheap jacket in San Jose that I was willing to destroy ($10) before I left. I slept in this jacket and spent every moment without the sun in this jacket. It's COLD.
Toiletries and Medical Supplies: There are no toiletries available at the lodge. Bring soap, shampoo, band-aids, tampons, whatever you're going to need. There is sharing between people, but who knows if someone will have what you need. Bring everything at a minimum and in small packages. Bring a small towel, too. Oh, and the water is FREEZING!
Camping/Beach/Outdoor Gear: I don't know if you can see it fromthe photo, but I am prone to blisters on my feet. MOLE SKIN IS YOUR FRIEND. Invest in a nice kit of Mole Skin. It saved my sanity. Have plenty of thick socks, and bring an anti-biotic and band-aids with you.
Miscellaneous: You have to bring your own food. Bring light things, like oatmeal, dried fruit (you'll need it for energy and potassium), pasta with sauce in pouches, and coffee or tea! I suggest hot chocolate as well. The water up there is excellent, so no worries there.
Clothing/Shoes/Weather Gear: If you hike up Chirripo, make sure you take a comfortable pair of shoes. Also, it is bitter cold in Base Crestones. I hiked during summer, yet the weather up there got as low as freezing. Take good thermal underwear and a good sleeping bag (they do rent good ones up there if you don't have one).