This paper aims to investigate characterize features of didactic contracts in realistic mathematics education teaching practice in Indonesia in the case of a lesson on addition. We just focus on some episodes of 26 first grade students and a female teacher from SDN 197 Palembang learning combinations that make ten based on a Palembang traditional food, pempek, and tablets of medicine. The result shows that some features such as formulation and validation appear during the teaching and learning process. The students are able to produce combinations that make ten individually and collectively, and also make agreement for those combinations. The teacher has an important role to guide students to the process of institutionalized knowledge.