Trying to join a multiplayer server and cancelling right after, gives you the items inside of a singleplayer world.

When joining my friends survival world I quickly pressed cancel before I got inside the server and then logged into my newly created world and it gave me the stuff I had on the multiplayer server. In survival the items disappear after they are interacted with or the player rejoins, but in a creative mode world, they keep the items and they don't disappear after rejoining.