You’ll notice that items have a number of options. The first is the item’s Repeat settings. Items set to repeat (the default) will remain until you delete them. Otherwise, they’ll be deleted once purchased.
The Auto Suggest options allow you to set the item to automatically set itself to “Buy” at either fixed intervals (Manual), or at an interval based on past purchases (Auto). (Auto items will only show a “Recommended” flag unless you set them to turn on in the Preferences.)
The Show In Lists section allows you to move an item to a different Main list. It also allows you to set the item to appear – when set to “Buy” – on an alternate list when shopping.