I keep it simple for my pups. My dogs have different personalities, so for one a trip to the Barkery (a dog bakery) because he loves to eat and he loves car rides so we take an extra long drive. The other loves fetch so a trip to a park with a new toy or ball, or maybe go on a hike.
I know a lot of people do cakes and such, but with low-fat, grain-free diets we are limited on that front.