Pete has a good list. I'm not a professional like him and I find myself waffling when thinking about this question. Could you describe your friend's situation a bit more? Because I think it gives us an idea of how much "professional" support and gear he might already have available. A few church members who are doctors, hopping on a plane to the DR then driving over the border to Port Au Prince is a much different situation than a doctor going as part of a established rescue/aid group.

By the way, anyone know the mosquito situation in Haiti? It's pretty hot there, so I would imagine that there are a lot of them buzzing around.

I wish your friend all the best. Let us know if he really does head out.