Welcome aboard, Nancy!
I have done small healthy snacks (as part of the healthy snack challenge) (e.g. pistachio, almond and other nut packs or different nut butter sample packs, dark chocolate bars/samples - 60% cocoa or more, water bottles, etc.). More recently, I did 2.5" smiley face stress balls (off Amazon) and scalp massagers (for the Practice Positivity domain). I have heard another Champion has done single $5-$10 gift certificates as an incentive for a single prize winner reward.
These have all been out of our own pockets, but I have heard of a department (per the Champions' advocacy) getting certain elected funds each quarter or year for Well-Being prizes before too. Another has cash rewards for a larger challenge accumulated from an entry fee (weight loss challenge).
Good luck! Happy Healthy Holiday's!