If she is in foal, as someone else said, find someone to be at your home with you so you can pay close attention to your mare, if this is her first foal, due to her being a first time mama, it is very important that someone is there in case something should go wrong.
Here are some things to do and/or have:
The vets #'s, both emergency and off hours
Iodine to dip the end of the umbilical in
Twine to tie the umbilical off
Flash light with new batteries
Foaling stall with a lot of soft straw in it
Blanket to rub the foal off or wrap them in if it is cold
I am sure others will be able to add to this list. Here is a very helpful web site that you can read and it may help you too..