I love the idea of three days of prayer centered around 3 American Feast Days (this is often called a triduum). I think about the three Feast Days of America that are centered on summer & our lives as Americans: Memorial Day, Independence Day and Labor Day. These are appropriate prayers for each of these occasions (from the BCP):
Almighty God, our heavenly Father, in whose hands are the living and the dead; We give you thanks for all your servants who have laid down their lives in the service of our country. Grant to them your mercy and the light of your presence, that the good work which you have begun in them may be perfected; through Jesus Christ your Son our Lord. Amen.
Lord God Almighty, you have made all the peoples of the earth for your glory, to serve you in freedom and in peace: Give to the people of our country a zeal for justice and the strength of forbearance, that we may use our liberty in accordance with your gracious will; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.
Almighty God, you have so linked our lives one with another that all we do affects, for good or ill, all other lives: So guide us in the work we do, that we may do it not for self alone, but for the common good; and, as we seek a proper return for our own labor, make us mindful of the rightful aspirations of other workers, and arouse our concern for those who are out of work; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.