Get lots of fruit and lay it out in front of you. I think grapefruit seems to work particularly well for this, but all delicious raw food. It triggers something primitive in me. I think it's the visual bright colours and the beauty of it, the smell/odour that's coming from them. Exercise as well.... and just doing anything you feel like doing. The feeling that this is YOUR food, and nobody can take it from you.
As corny as it sounds, sometimes I feel so happy when I have lots of lovely fruit in front of me that I feel like crying.
I think it triggers something primitive in us. It may not work as well if you already ate poor foods earlier in the day.