Dave, how nice that you want to surprise your wife with something onboard! Depending on how much you want to spend, choices range from $10 for chocolate covered strawberries to $700+ for one of Royal Caribbean's "Romance Packages" that include champagne, canapes each evening, breakfast in bed one morning, spa services, etc.
Take a look at some choices here
to get an idea of the kinds of things you can do, from culinary treats to wine to those Romance Packages. Maybe something will strike your fancy.