Belgian Tripel is a flexible style, with a lot of possible additions, but some really bad combinations.
A Belgian Tripel is a good base style for a boozy ingredient. Ingredients like bourbon and whiskey would blend well.
Fruit flavors are a good match for a Belgian Tripel. Berry flavors including blueberry, raspberry, blackberry, and strawberry would work with the fruity esters of a Belgian Tripel. A Belgian Tripel is an okay base style for a citrus flavor. Ingredients including cherry, grapefruit, and orange peel maybe would work. Tree-fruit flavors like peach and plum likely work as well.
Flavors like lemon grass and hibiscus would work with the tart flavor of a Belgian Tripel.
Surprisingly, a Belgian Tripel is an okay base style for a nutty addition. Ingredients including hazelnut, pecan, and coffee would work.
Despite it having a spicy yeast character, a Belgian Tripel is only an okay base style for a spicy ingredient. Flavors for instance chai, seeds of paradise, ginger, and peppercorn would likely work, but a Saison may work better.
Herbal additions work, with green tea likely working, or a more floral addition like elderflower.
BJCP Style: 26C