A storage unit for a refrigerator door includes an adjustable retainer assembly that can be positioned to accommodate food containers having varying widths. The storage unit includes a bottom portion and opposing side portions that define a storage cavity. The retainer assembly is sized to be received by the storage cavity. More specifically, the retainer assembly includes a base member that includes a bottom portion and opposing side portions. Each of the opposing side portions is provided with an adjustment elements. The retainer assembly also includes a retainer bar that includes a retaining surface that extends to two opposing side members. Each of the opposing sided members includes a detent element that enables the retainer bar to interconnect with the base member. In this manner, each of the opposing side members can be independently adjusted relative to the base member in order to conform to food containers having varying widths.