Nally,
It really depends on what you have in the house.
How about a nice dinner - small steak/chicken breast, lots of veggies, salad, candle light, soft music?
How about a SF jello/FF cool-whip type dessert in a pretty glass? Or a ricotta dessert?
How about a nice backrub or umm some other "special" favor
You could also let him know how much you appreciate him and are proud of him for changing his lifestyle with you.
I know you will think of something to make his day special.
Kim