In the field of sensor networks cross-layer interactions are favored over strict layering of components and regarded as a way to provide the optimization capabilities required by sensor network applications. Despite their importance, developers tend to devise specific solutions for the application at hand, instead of designing more general primitives that can be used across applications. The contribution of this paper is twofold: We analyze several typical sensor network applications and provide a classification of the types of cross-layer interactions found in their code. Based on this classification, we propose TinyXXL, an extension to the nesC language that defines primitives for seamless cross-layer data exchange.