Abstract: An activity bag system includes an outer carrying bag, multiple interchangeable inner containers carried one-at-a-time within the outer bag, and a container storage cover for each inner container which also serves as a partition for the outer carrying bag. Each inner container is divided by partitions into compartments for carrying the items needed for a particular sport or activity. At least some of the compartments are covered by a lid to which some items can be secured. The outer bag includes a lower section which receives the inner container and an upper lid section separated from the lower section by the inner container's storage cover. The inner container is placed within its storage cover when not being carried by the outer bag. The outer bag includes straps for securing large items to its outside surface and outside storage pockets, including an insulated pocket for carrying a container of hot or cold liquid.