The LDS Church Missionary Department recommends the following, which is included with every missionary's call:

Sending additional funds for emergencies or other reasons

"The preferred way to send funds is through a personal debit card, which the missionary sets up with his or her personal account before arriving to the MTC. Simply deposit funds into the debit card account. These additional funds should be minimal. The card can then be used by the missionary to obtain local currency from automatic teller machines or bank offices in the mission, as well as for purchases and cash advances at most businesses. Please make sure the card will not expire during the mission."

Health care not covered by the Church

"Elective procedures: You will be responsible for paying for elective procedures, which are defined as any medical, dental, or eye care that is not associated with sickness or injury."

"Dental injuries: Dental expenses that arise from an accident in the mission field and are not covered by your insurance will be paid by the Church." Note that dental expenses not associated with an accident are not paid by the Church.

Deseret First can help you set up a debit card that will make it easy to be prepared for financial needs that may arise while you're gone.