This is the best idea and I snagged it from my soon to be 80 year old mother-in-law. While at her house over the holidays I noticed this simple trick she used to keep her trash bag from sinking to the bottom of the trash can!
My mother-in-law used two magnetic office supply clips and attached to each end of the trashcan. The grip is tight enough that the bag doesn’t “drop” into the trashcans. My kids are known to ignore the sinking trash bag and I end up with a mess at the bottom of the can. After a week in practice, it totally does the job of holding the bag in place!