1. A computer-implemented method comprising: receiving, from a client device authorized on a user account of a content management system, an amount of free memory space available on the client device for caching one or more content items associated with the user account; defining a subset of the amount of free memory space available to use for caching the one or more content items; selecting a subset of content items from the one or more content items associated with the user account based on the subset of the amount of free memory space on the client device; increasing the defined subset of the amount of free memory space to use for caching based on a measured stamina of the client device; and selecting a further subset of content items from the one or more content items associated with the user account based on the increased defined subset of the amount of free memory space.