I didnt think you were allowed fruit on the intensive stage of optifast?? Only on maintenance?
When i did optifast (and the reason I stopped is the same you are mentioning now btw
i used difference essences in the shakes...you can get them in the cake mix/jelly/ toppings aisle of any supermarket....i used to like - chocolate shake with orange essence (tasted like a jaffa) or choc with peppermint essence...vanilla with strawberry was nice... you can get banana essence, coffee, anything at all, and that really helped me
They are about $1.00 per bottle, with the food dye and that type of thing
Im sure you could get a more extensive range from a baking shop too
Good luck with it