This activity can be adapted to a number of learning goals and many other materials can be used incl shaving cream. Read Practicing Sight Words With a Salt Tray at
Very detailed framework, useful for ELTs at http://www.languageartspress.com/ceq/A%20Framework%20for%20Using%20the%20Prepositions%20In%20and%20On%20-%20CEQ%20-%20Fall%202017.pdf
Find them here:
Find them at http://www.engames.eu/teaching-vocabulary/
Interesting terms discussed at http://www.quickanddirtytips.com/education/grammar/placeholder-names-thingamajigs-doohickeys-and-whatchamacallits
What phrases work best?