Air conditioning is barely starting to come into the society at large. Winter is mild, and there is an occasional snow fall every couple of years. The mornings can get pretty low, but it is rare to see it below freezing during midday in the very dead of winter. A suit coat is generally all that you need, however it gets reasonably cold in the morning and at night, so prepare yourself to your preference. A v-necked sweater to put under your suit or something to put over your suit coat will be greatly appreciated.
Gloves are nice.
French scriptures will be given to you at the MTC as well as plenty of french study materiels. Bring your english scriptures, or scriptures in your native tongue. You're coming to one of the most beautiful areas of the world. Bring your camera so that you can share this beauty with your family and keep the photos for your memories when you get home. Do bring a small handheld cassette tape player.