These are a few items that the newcomer might not think of. Some of them will apply to everyone, but not others, depending on what kind of place you live in. They are available for purchase in Haiti, unless noted otherwise.
Buckets. You will probably need more than one of these. A bucket is not just a bucket. It is a hand washing station, a shower, a water-drawing tool, a trash can, a storage container, a mop bucket, a measurement tool, and so much more.
Rope/String. The first thing you'll need it for is lowering your bucket into the cistern to draw water. But there will be many other random unexpected uses for it, like holding your broken crib rails up, rigging a system to mount your mosquito net when you don't have a hook in the ceiling, or tying strings to the balloons (that you brought from the US) at your child's birthday party.
A propane/gas stove. Because it works whether you have power or not.
A hand-held fan. Nicer than fanning yourself with your Bible during church.
To be continued as I think of more items. Feel free to suggest other things in the comments!