Ws sis
It would be a good idea to keep a record of the dates of the period of work. Its really useful if you are able to do regular volunteer work e.g. I used to volunteer at the local hospital every monday for a year... and then formed good contacts for referees later on. If the staff is familiar with you, they maybe more likely to take you on for a part time job in the summer or something.
Keep a record of your main roles and responsibilites, the skills you acquired and any other relevent experience. If you can help with something like translating, then do so... and let the staff know if you think your able to help in other areas. e.g. I had experience in feeding and taking care of elderly patients in a nursing home, so they let me get more involved in the hospital wards. They gave me more to do than the average volunteer and its all useful in building yourself up as a person which can be reflected in your personal statement when you come to applying for medicine.
Make sure you talk to the person authorising you as a volunteer about references etc before you leave. And finally enjoy it...its great fun!
Ws x