I am assuming you are planning this with only your troop and not with the neighborhood?
Is your troop going forward into Brownies?
If you have troop money to spend you can buy the vest and give them their #'s (sew on or attach) & give them a brownie book after they cross a "bridge". (or parents could buy it for the bridging as an option)
It was really cute for them to put on their vest after they crossed the "bridge", it really made them feel special and grown up. We just put it on over their Daisy vest.
We had made a bridge out of helium balloons once. Tied them to rocks. Lined them up on each side.
The girls could even make there own bridge somehow.
Another time we went to a park and used their bridge.
Have the girls plan the bridging ceremony. Pick out songs, poems, or skit.
Do the Pledge and the Promise as an introduction.
Oh our girls wanted as the snack, yep you guessed it, Brownies!
Have fun planning!