Now where do the bingo chips, bottle caps, glue gun, double sided tape and foam sheet come in?
They are for elevating the framed painting off of the wall.
Walls perspire or at least can seem to. You can test this. Look for a wall that has an air conditioned room on the other side. Place your palm against this wall. It feels cold and sometimes condensation even form on your side of the wall. Now imagine what can happen to a painting that hangs on this wall. It can accumulate moisture just from surface to surface contact over time.* By elevating the painting a fraction using bingo chips or with plastic bottle caps discretely placed at the back and out of sight, you not only minimize surface contact with the wall, you increase air circulation at the back too. This keeps your back panel drier. Since I started doing this a decade or so ago, I have never had problems with molds even during the very wet rainy season.
*Aircon test was shared by Kermit, master craftsman at my favorite frame shop in Bataan – Gerard’s Frame Station.