Water is KEY. Keep them in cold water AS MUCH AS POSSIBLE. Driving to and from places, or when you aren’t using it are great times to shove that beautiful bouquet in water to keep it lookin fresh;) Literally any time you can put it in water, do it!
With boutonnieres, corsages, and flower crowns, they have no water source, so putting them back in the box and spraying them with water before the reception is a good way to keep it fresh. A LOT of groom boutonnieres are DESTROYED after the ceremony before the reception from lots of hugs, I always tell my brides to consider getting two for at least the groom!
If you are picking up the night before or have a while before usage: Fridges are usually okay for flowers, but sometimes can be too cold! Flowers like it best between 34 and 36 degrees. So, if your fridge is too cold or you don’t have enough room, place the flowers out of direct sunlight and somewhere cool as much as possible leading up to the event.