For realizing intelligent sensing adaptive to various scenarios, flexible and integrated electronics with multiple functions, without sacrifice of electro-chemical properties, are urgently needed. In this work, we rationally design a multifunctional, high-conductivity, flexible, anti-freezing and self-adhesive double-network hydrogel with a three-dimensional (3D) interpenetrating framework. The hydrogel is capable of stretching up to approximately 1100% and can be utilized directly as a piezoresistive strain sensor, the electrode of a self-powered triboelectric nanogenerator (TENG), and the electrolyte of a supercapacitor (SC) concurrently. The self-powered and stretchable TENG generates high electrical output, thereby being capable of sensing low-level human biomechanical activities in real time. The assembled SC deliveries high capacitance at a broad range of current densities in a wide temperature as low as −20 °C. By integrating the self-powered TENG with the flexible SC into an integrated self-charging power supply system, this wearable and flexible system can harvest normal activity of the human body, realize high-sensitivity biomechanical sensing, and store the excess energy in the SC to supply continuous power for small electronic devices when needed. This work provides a promising pathway to the assembly of a wearable and self-driven system for self-powered round-the-clock health monitoring.