I had no idea that today was the Nativity of the Theotokos.
Obviously, I was unable to attend services. How could someone keep a feastday without attendance at church?
Frankly, if you were not aware today was a feast day, I would start familiarizing myself with the upcoming feast and fast days. And if you are attending a specific parish, become more integrated with the parish, so you know what services are on the horizon and the like.
Probably most folks can't make a DL in the AM in America. We had a vesperal liturgy last night and an Akathist to the Theotokos this morning (not a big crowd).
This probably ain't the answer you were looking for, but I think it would be wise.
Aside from that you could read the portions of scripture appointed for the day. A narrative of the Theotokos' Nativity. Read portions in the NT where the Theotokos speaks.
Maybe see you can find the hymnography for the DL to get an understanding of the typological approach to the OT in light of the Theotokos. Read an akathist to her.
I wish I could pile up links for these resources for you, but I think others can and you can probably google some of the material yourself as well.
Oh yeah, Rejoice!