As much as I love to buy cut flowers, it always upsets me to see them wilt so quickly. My solution to this problem is a quick trip to the nursery, where I buy plants meant for the garden, you know the ones that are sold in those 6 pack containers.
At home, I pick a pretty container, line it with some plastic cling wrap and basically pot the plants in a nice arrangement. The plants usually last a couple of days in this manner and are replanted in the garden the minute they start to look a bit stressed.
Try it out, this way you get to enjoy your centerpiece selection for months to come!