The weather should be fairly warm mid-September but it will be an outdoor wedding. So consider bringing layers.
The ceremony will take place outdoors in the grass, so reconsider pointy heels. The cocktail hour and reception, however, will be on flat ground. More comfortable shoes suggested!
Gifts the day of the wedding are not necessary. Consider ordering directly from the registry if you wish to purchase a gift. Otherwise, there will be a box for any cards or cash gifts.