Either get your child to collect the things they find and bring them back to you or you could let them take photos on your phone once they find them.  If you get them to physically make a pile of goodies, offer them a treat if they put it all back where it belongs or offer them extra points if they are versing a sibling.  You can even extend this and make it a timed challenge.  Get them to repeat finding another item that fits the description and see if they beat their time.  If your child doesn’t read you will need to direct them, but for kids who can read this will add to the challenge.