I have a long running conversation with ChatGPT that I use to keep track of a verbal to-do list. I tell it my items with categories (e.g. work, personal, etc.) and estimated times, and then it outputs my complete task list, grouped by category. I then just tell it when I add tasks or complete tasks, and it continually keeps track of and outputs my current outstanding task list.
I've been using this for weeks now, and since it's all in a single conversation ChatGPT can keep track of the entire state over time.
I don't have access to plugins yet but it would be trivial to implement a personal AI assistant with ChatGPT if it could, for example, look up flight times and prices.