DS is finishing his plebe year at USNA right now. Membership in a parent's club is not mandatory. I joined our local club because it is a way to stay updated on the various service academies. ( DS doesn't give me a lot of info about anything.) The clubs are open to any parent who has a child at any of the academies, not just USNA. Each club is probably a little different depending on the number of members. In our club , siblings can attend meetings as well. Our current club president has contacts at all of the academies. Parents share general info that we hear from our kids, nothing real personal. Parents can also ask questions of other members. I know there are several clubs elsewhere in the country that will have cookbook sales as fundraisers, etc. Our club is kind of small-we don't do that.
We meet 3 times per year- we send USPS boxes of treats to all the service academy students from our area a week or so before the following: Halloween, Valentine's Day, and finals week. Parents usually buy the treats in bulk at places like Sam's Club, Costco, etc., and part of each meeting is spent filling all the boxes assembly line style. In addition, each year, the club sponsors a congratulatory , catered sit-down send-off dinner to all academy appointees in the incoming class.
It is nice to meet other parents who also have children attending the same academy- to realize you are not alone, and to hear what is going on at the other academies.