With the decentralization of the energy supply, district energy management with sector-coupling gains importance, as we urge towards a fast reduction of greenhouse gas emissions and aim at more efficient energy usage. By jointly optimizing and coordinating the electricity, mobility, and heating domain, the share of local renewable energy share can be increased, and costs can be decreased across sectors. The paper mathematically describes a joint Sector-Coupled District Energy Management (SeCo-DEM) as a multi-objective mixed-integer linear program. The model includes combined heat and power, immersion heater, energy storage system, hot water storage, a peak-load boiler, and bi-directional electric vehicle chargers. Based on data from two research projects, we analyze the individual influence of different flexibility options in terms of costs and self-consumption. We find that combining bi-directional charging and an immersion heater is a cost-effective combination that can increase self-consumption from 68.14% to 93.70%.