Don't say as a cashier at Target. They want you to show ambition. Don't be too vague, but don't be awkwardly specific. Stick to "as a graduate student, working toward my next degree" or "in a position of management, teaching others". It's okay to stretch a little. If you're not comfortable giving definite answers, use the words "hopefully" instead of "maybe" and smile when you say it, like you really hope it'll happen!