There's lots of things you could do. Imagine you're making a group chat bot (way more difficult than a 1-1 chat) where people can play social games by giving the LLM game rules. You can have an agent that only manages game state using natural language (controlled by the main LLM). You could have an agent dedicated to remembering important conversation, while not paying attention to chit-chatting
What more functionality do you need than the system prompt and list of tools?