Each year I pick out one color and I use that trim for the entire room, yes, the entire room! Your students and parents will love what you put ON the bulletin board. They will not go home thinking, "That Mrs. Smith, she used all red trim this year."
When you use one color for all your boards, you will never run out of one little, last piece. If a student trips and grabs the board, ripping some off of the bottom, you will have back up trim left over!
No stress of running to the store right before school starts because you ran out of a certain pattern for a certain board!
I have a Pinterest Board just for Elementary Bulletin Board ideas, click here to see it.