This is new content in the second edition of Praying the Mass: The Prayers of the People, Chapter 9, "Offertory Prayers".
The bread and wine are blessed by these prayers; they are set aside for the Eucharistic Prayer, when they will become the Body and Blood of Christ. But in that brief time between the Offertory and Consecration, the bread and wine are sacramentals because of the prayer of the priest over them. A sacramental, such as the bread or wine to be used in the Eucharistic Prayer, or a paten or chalice, is dedicated for a particular use when blessed. This is not the same as the change that takes place in a sacrament (such as the Eucharist), where bread and wine change ontologically (that is, in their substance). A sacrament involves a change of being, whereas a sacramental involves a change of purpose.
By uniting our spiritual sacrifices to the bread and wine in the Offertory, we “appropriate” those sacramentals, much in the same way we “appropriate” holy water (another sacramental) by being blessed with it, or we “appropriate” a blessing over a meal by praying it. We join our spiritual sacrifices to the bread and wine (which represent, physically, those very sacrifices), imbuing them with a greater spiritual significance for each of us and for the Church as a whole.