Can 501(c)(7) members buy optional goods and services from the social club, where other members might abstain?

I understand that, typically, 501(c)(7) ("social clubs") charge their members dues. However, after reading the IRS’s documentation, I am not clear about their stance on members voluntarily contributing more revenue/receipts to the organization, such as with merchandise.

Say the club has 100 members, each member has paid their $50 dues for the year. Say 2 members now want to purchase t-shirts from the club, which cost $40 each. None of the other members (the other 8) want to do this.

Is this allowed? Or does this "inure to the benefit" of a subclass of members in some way, and somehow place the club at risk for losing its tax exempt status?