Since there is no set liturgy for the ritual and no Jewish law dictating the ritual's contents, there is a great deal of variety in Tu B'Shvat seders. During the seder service itself, the seven species for which the Land of Israel is praised in the Bible (figs, dates, pomegranates, olives, grapes (or raisins), wheat and barley) generally play staring roles along side the four cups of wine. Following the service itself, almost anything seems to go. I've had pita pockets and hummus (after the seder with my daughter's first grade class), luscious fruit desserts (after the late night seder in my synagogue), and full course meals (following the seder at my friends' home). I think the ability to be creative is one reason for the increasing popularity of Tu B'Shvat seders.
If I had to pick a basic Tu B'Shvat recipe, I'd pick the 15 Fruit Salad that my friend Elise Rynhold brought to us last Tu B'Shvat. Tu B'Shvat is the 15th day (Tu) of the Hebrew month of Shvat (B'Shvat), so Elise always makes a fruit salad that contains 15 different kinds of fruit in honor of the holiday. Elise's 15 Fruit Salad is the tastiest fruit salad I've ever eaten.