Also known as communion patens.
Are they optional? So it would seem, given that in many places you will never see them being used. However, here is what liturgical law has to say about the matter:
General Instruction of the Roman Missal (GIRM)
Heading: “Things To Be Prepared [For Mass]”
118. Likewise these should be prepared:
a) next to the Priest’s chair: the Missal and, if appropriate, a hymnal;
b) at the ambo: the Lectionary;
c) on the credence table: the chalice, corporal, purificator, and, if appropriate, the pall; the paten and, if needed, ciboria; bread for the Communion of the Priest who presides, the Deacon, the ministers, and the people; cruets containing the wine and the water, unless all of these are presented by the faithful in the procession at the Offertory; the vessel of water to be blessed, if the sprinkling of holy water takes place; the Communion-plate for the Communion of the faithful; and whatever is needed for the washing of hands.
It is a praiseworthy practice for the chalice to be covered with a veil, which may be either of the color of the day or white.
Instruction “Redemptionis Sacramentum” (2004)
Heading: “The Distribution of Holy Communion“
93. The Communion-plate for the Communion of the faithful should be retained, so as to avoid the danger of the sacred host or some fragment of it falling. [And the footnote references the above number of the GIRM.]
Fortunately, they are also not expensive. Although the sky’s the limit, you can get these basic ones for just $30 each. It should be possible for every parish to have a full set at that price. Especially if their priorities are in the right order. Sometimes we devote more money and attention to things that are not nearly as important.
See also my post about Communion in the Hand.