The beauty of loose parts is they can literally be anything, promoting creative thinking. Because the 'parts' are not prescribed as something the play time can be open ended- there is no right or wrong thing to do with the items (encouraging a child to develop their concentration span).
We have a rather large collection of shells , to which we added some glass beads. I presented them along with a mirror in some glass jars.
The Frog played with them and enjoyed making patterns, empty and filling the pots. Playing with the items on a mirror The Fairy spotted the play set up as soon as she arrived home from school. Her shells were people and the glass beads we the sea. She created a whole narrative with the loose parts as props.
Do you have a favorite loose parts toys?