(Trivia bit which I have gathered from novel reading: In Cornwall and perhaps other parts of England you are not supposed to eat blackberries after Michaelmas on pain of illness and possibly death. Something to do with witches. Okay, end of trivia digression.)
I'm surprised to see that I never seem to have put up the BCP collect for Michaelmas. This was remiss of me, as it seems to me to embody Cranmer's approach, which I find very congenial, to such holy days. Both my Catholic and my non-Catholic readers will notice both what Cranmer says and what he does not say. But hopefully both will acknowledge that this is great liturgy:
O everlasting God, who has ordained and constituted the services of Angels and men in a wonderful order; Mercifully grant that, as thy holy Angels always do thee service in heaven, so, by thy appointment, they may succour and defend us on earth; through Jesus Christ our Lord. Amen.