I know I've written about this before, but if you plan to do your own wedding flowers, you may want to pick something that can be done a few weeks or days in advance. Floral arrangements usually have to be put together the day of or the day before the wedding, otherwise they die or wilt and just look ugly. Nobody wants ugly flowers.
An alternative? Succulents! I've also written about succulents before, but their compact structure, easy care, and hardy nature really make them ideal for the DIY wedding. They can be assembled early on and you can actually be very creative with them. For example, this bride has her bridesmaids carrying small, potted succulents. Pretty awesome! Check out all the pictures (it's truly worth it) at Jesi Haack Weddings.