Back when we toured a local historic farmstead, a musician was playing out of tight little hardcover music books from the 1800s. He kept them open with large wooden clothespin-looking things. I couldn't concentrate on his talk because I was staring at the wooden pins.
I love to play hymns out of my hymnals where I jot notes to myself on the margins, but it was a perennial problem to keep the hymnal open. I was always propping it under books or grabbing at it as it flapped shut midway through the song. I don't like to use the spiral-bound hymnal for accompanists at church (no notes!) and I don't want to make photocopies (an avalanche of paper!).
Clearly, I needed those wooden pins or their equivalent.
There are giant binder clips, but the ones I found were about $10 apiece. Then, one day in the local art store, I came across large silver clips for $1.25 apiece.
They work! They are large enough to handle the biggest hymnal I have, and I am so pleased. I haven't seen this solution among the musicians I know, but perhaps this is a common trick for professionals and I just missed it all these years.