Candy
From PinataIsland.info, the Viva Piñata wiki
What would Piñatas be without candy? Each species has their own pinata fillers. Piñata love eating candy and every piñata in the game has a distinct candy themed after the animal, so the bee’s candy is bubblegum for example. Other Piñatas want to eat other piñata’s candy as part of the food chain. They break it open and snarf it down. You can also break open a pinata with your shovel. The broken piñata then reforms and leaves your garden because it doesn’t have any candy left. Then there are also the bad piñatas, called sours and they’re full of bad candy...you don't want your piñata to eat that candy. Candy can be obtained from a broken pinata and sold for currency.