A customizable bag organizer is an apparatus that organizes and supports the structure of a bag. The apparatus includes at least one organizing mechanism. The at least one organizing mechanism includes a central rod and a plurality of telescopic dividers. The central rod connects each telescopic divider. Each telescopic divider includes a fixed panel, a free panel, at least one first track and at least one second track. The apparatus includes a base plate to uphold items within each compartment defined by the plurality of telescopic dividers. In order to easily see within each compartment, the apparatus includes at least one light source, a light sensor, a portable power source, and a switch. The items within a bag are removed while maintaining the desired positions within each compartment as the apparatus includes a supplementary pouch. The supplementary pouch upholds the items, the central rod, and the plurality of telescopic dividers.