In my opinion…
Supplemental funds provided by a parent depends on the "maintenance" level, high or low, of your child. They are issued a standard set of items that they pay for out of their loan and ensuing salary. Theoretically, a person can exist on the issued items, services, and remaining pay they receive.
Although, there may be plenty of other things that can be categorized as "must have" or "nice to have". For example…
1) Alternative food, i.e. Iron Rooster, Sofi's Crepes, Annapolis Ice Cream, Federal House, ACME, Chick and Ruth's.
2) Alternative travel, i.e. Visits home, Spring Break, Uber, airport shuttles, car expenses (upperclass).
3) Alternative recreation, i.e. PlayStation, X-Box, movie tickets, sports gear.
4) Alternative style, i.e. Spirit wear, Under Armor swag, hair care.
5) Alternative energy sources, i.e. Caffeinated beverages, workout supplements.
I believe that this is where the concept of fiscal responsibility comes into play. That is, living within your means.
Being a Mid is the first step to becoming self sufficient. Essentially, it's a job. They are paid and have responsibilities. Other than their USNA responsibility of being satisfactory or "SAT", their personal responsibilities should include…
1) Securing financial and personal enrichment, i.e. barter and trade of acquired goods (issued items), making alliances (friendships).
2) Taking care of personal belongings, i.e. decreasing the risk of damaging or loosing acquired goods.
They will start making their own choices. These choices will guide their future.
As a parent, I believe there is a delicate balance in the support you give your child. They will need emotional and financial support throughout their lives, whether it comes from you or elsewhere. The actual amount you provide may vary based on ability, personal preferences and stages in life.
Awhile ago, Keith Richards and Mick Jagger noted that, "you can't always get what you want, but if you try sometimes you might just find, you get what you need."