The same goes for the toys you leave for cats to play; just click on “goods” and pick some items to leave out. Some items are large and can only be placed in the middle. (With version 1.3, they’ve updated the items with “S” and “L” icons to indicate which items are small and large respectively.)
For reference, here is a screencap of an extended garden (with the default theme) to show you where food bowls and items are located. The location of food bowls and items WILL change if you change your theme.