Carrots! Buddy's crazy about them. I ran out of treats and had a bag for the rats in the fridge, and on a whim gave him one. Now every time he sees me with them, he goes into full on begging mode, and they're our preferred treat for training and picture posing bribery.
This is a dog who's focus is so bad that I've left training sessions in frustrated tears while he happily chased a leaf, deaf to the world. But nothing can break his gaze from that carrot!