What sort of personal equipment do you find necessary to bring on a medical trip to a third world country or disaster relief area?

This question is too broad. A medical mission to a developing nation is not the same as a trip to a disaster area, and would necessitate making different choices.

A useful answer would depend on too many factors such as the climate, length of stay, the security situation, the likely health risks, and personal interests. Would you be part of a large, well equiped team, or just winging it on your own.

Narrow your question so we can get in the ballpark.