I think being equal in heavenly things refers to membership in the Church of the Firstborn, joint-heirs with Christ. Being equal in earthly things, under the law of consecration, means we abide the law in the proper spirit. The terminology in D&C 51 is, "every man equal according to his family, according to his circumstances and his wants and needs." So context, circumstance and subjectivity are considered as well as quantity of goods, requiring a high degree of spirituality to live "after the manner of happiness" (2 Nephi 5: 10-17, 27); as no happier people, having the love of God in their hearts (4 Nephi 1: 15-18); and following the principles of Zion where there are no poor among them.