I think an example from Cookie County on giving players agency was the ability to destroy snowmen. I added this feature on a whim and wasn't sure if it seemed cruel to be able to destroy your little snowmen, but then I realized while watching playtesters play that it influences how they play because it forces them to avoid hitting them. I wish I could've added more features like this because it makes players feel like they are really affecting the world, even more than just turning on lights. Having a game world that reacts to player actions really drives home the sense that your choices as the player are meaningful and contribute to a more engaging experience. Hope this helps :D