Another designer and I worked on a team to create a personal finance app concept aimed at Millennials, focusing on creating a fun experience to connect budgeting to personal financial data. Instead of breaking finances into many specific categories, we chose to approach the app's budgeting structure by separating needs from wants (core, mix, and fluff).
The Core category identifies expenses that are necessities and recurring costs, such as rent and utilities. The Fluff category identifies expenses that are non-necessities, helping the user mentally separate the things that they know they need from the things that they want and are not obligated to purchase every month.
The Mix category holds items that can vary in cost and importance, identifying areas that the user can easily save money by limiting extraneous expenses that are only pseudo-necessary. For example, a student could know that they need food, but easily spend more than planned on spending in a given time period by eating out instead of cooking at home. The critical Mix category helps aggregate these expenses and offer tips to limit spending.
The Other category identifies unexpected or unusual expenses that are still necessary, i.e. a car repair.