Is it possible to copy food items from one day to another? Also are you able to copy the entire previous day food items to the current day?
You can copy items. I'm not sure I've done it on the mobile app, but I think it is possible. On the web, you can select the items you want to copy then choose "copy selected items" from the vertical ellipsis menu at the top right corner of the diary. Go to the day you want to copy to and choose "Paste" from the same menu.
If you want to copy all items (not just food items) from one day to another, it is even easier. To copy yesterday's entries to today, select "Copy Previous Day" in the vertical ellipsis menu. To copy a different day, go to that day and select "Copy Current Day" then go to the day you want to copy to and select "Paste".