A small knapsack or bag will come in handy. A dress or two for special occasions. Shorts may be worn, but short-shorts may elicit unwanted stares and whistles if worn downtown. A sports jacket and a tie maybe. Toiletries can be bought in San Jose, but bring enough.
Drugstores have a good supply of imported goods, but are expensive.
The Costa Rican monetary unit is the Colon. It is always a good idea to bring some dollars to tide you over until you can go to the bank to exchange dollars. Don't expect to cash personal checks. Major credit cards are accepted in mostlarge stores or hotels in the larger cities. When you get to school, you may ask where is the best and fastest way to change money.