I have the Evolve Charm, and I want it's effects, but I'm not sure if I have to hold it or not. Right now, I'm holding the Red Bow, and I don't want to lose the stat boosts from that. It'll be a dream come true if I can just keep it in the bag.
When in the treasure bag, they help party Pokémon in different ways.
Source
Sounds like it only needs to be in the bag.
Hope I helped!
