While debated, the Moulid Abu el-Haggag is usually considered an example of a remnant of Ancient Egyptian religion in modern-day Egypt.

In Ancient Egypt, the Opet Festival was held for the deities Amun, Mut and Khonsu as their statues made a ritual journey by boat from their shrines at Karnak to the temple of Luxor.

Afterwards the statues were kept at the temple of Luxor for 24 days while the festival went on. They were then returned via the same route to Karna.

On the other hand, the festival of Abu el-Haggag is held in Luxor around two weeks before Ramadan. The steets of Luxor are filled with merchants selling toys, sweets and various other festive goods. Various bands and dancers perform everywhere.

A procession is then held with various boat-shaped floats parading throughout the city, attracting thousands of spectators each year who hope to get blessed by Sheikh Abu el-Haggag as the floats pass by.

Both festivities share the idea of a religious figure being celebrated by a parade of boats/boat-shaped floats in the streets of Luxor.

Sources:

Strudwick, N. and Strudwick, H. (1999) Thebes in Egypt: A Guide to the Tombs and Temples of Ancient Luxor. Cornell University Press

Johnston, S. I. (2004) Religions of the Ancient World: A Guide. Harvard University Press

As a related question: Are there any traces in Egyptian "folk Christianity"?

An obvious one is the family tomb. Egyptians, Muslim and Christian, continue to bury to their dead in tombs shared among their family members.

Another one is the tradition of leaving food at tombs after visiting a cemetery.