Place the floral bouquet, blossom-side-down, into the paper grocery sack. Don't allow the blossoms to touch the bottom of the sack. Instead, hold the stems out of the bag.
Wrap the grocery sack around the stems of the bouquet, still making sure to keep the blossoms off of the sack's bottom.
Bind the stems and bag together with a rubber band. This keeps the flowers from touching the bottom of the bag so they can dry evenly.
Place the sack on top of the paper plate. Place the paper plate somewhere cool and dry such as a pantry. Let the bouquet sit like this for a week.
Remove the dried, preserved bouquet from the bag and use as you desire.