When I have demoed the use of agents, I usually do it with an agent combining multiple applications' results. Something like: "We're having a family gathering at grandma's. Which of us can stop in at the drugstore to pick up her prescriptions on the way without adding a lot to our travel time?"

Agents are great at moderately complex combinations of data and apps. If I had to do this every day or every week even, it might be worth creating a script suited for a task like that using some automation system. Agents are great at providing a disposable saw when it doesn't make sense to stop and sharpen the saw.

I'm not a doorDash user, but they've been doing it long enough to have an app that's probably highly polished. There's not going to be a lot of upside to speaking or typing an English language command to get what you want. Trying to do that is a waste of a well designed app and the agent's token budget.