I never, ever reward myself for staying on plan with food - to me, that is hugely counter productive.
I have, however, been known to SHAMELESSLY bribe myself to stay on plan. Usually, the reward is a massage, I love them!
I set 10 lb rewards for myself as I was losing weight. I remember them all
180 - fancy sandals that were way expensive (they are now too big, who knew I would lose weight in my feet?) Oh well, I enjoyed them at the time
170 - massage
160 - new clothes (everything was sliding off me!)
150 - fancy cut/color at a very "ooh la la" salon
140 - massage (I had the same person! she noticed!)
130 - tattoo