Techniques are described for managing preloading of data for client computing systems. A client computing system may provide one or more persistent data storage caches on local storage, such as to support a particular software program executing on the client computing system (e.g., a Web browser program, with the persistent data storage cache designed to store browser cookies and other data for later access by the Web browser program). Additional data may be stored in such a persistent data storage cache by preloading those data groups before they are requested by the client computing system (e.g., based on interactions of a user of the client computing system with an executing program on the client computing system). Particular data groups to preload may be selected in various manners, including to provide a specified type of minimum functionality to a client computing system based on the preloaded data groups.