Before they announced the winner I asked the class to think about giving their pizza to a family who needs an extra meal if we won. I let them know that it would not be expected of them and nobody would blame them if they wanted to eat the pizza, because after all, they would have deserved it.
The next couple of days kids would come in the class and tell me things like, "A family who needs help can have my pizza". You can tell they were really thinking about it.
When it came time to send in our numbers of items we collected I asked the kids to put their heads on their desk and we would take a vote. 5 kids wanted the pizza party (who can blame them) and 16 kids wanted to give their pizza away. I was so proud of them.