I also don't know Jack & Sunny's birthday so celebrate the day I brought them home from the shelter, to me that has become their birthday.
I usually buy an assortment of treats and posh foods, as they don't have that normally as it's very rich. They enjoy it for a treat though. Last year they had a tin of red salmon between them and they love it! I also bought a turbo ball toy and other small toys too, that they love.
But most of all I think cuddles and loving is the main thing, though we do that all year round of course!