The common food ingredient was not used for Passover. What is it?

The ingredient is leaven (yeast). Hebrews remove all yeast from their houses before passover.

Source:

Exodus 12:16

What was the signal to the Angel of death to pass over the Hebrew houses?

The Jews marked the side posts and the upper door post with lambs blood. This can be done today but it is not required

Source: Exodus 12:7

What do the feasts of Passover(unleavened bred), Pentecost, Feast of booths have in common. That is not shared with other feasts. What do they have in common?

On these three festivals all males were to travel to Jerusalem and appear before the Lord,

Source:

Deuteronomy 16:16

Passover celebrates a holiday when a plague affected the Egyptians but did not affect the Israelites. What was the plague?

The plague was the death of all firstborn of Egypt. This affected both men and beasts.

Source:

Exodus 11:4-6

What did God say about Passover and the Hebrew calendar?

Nisan the month when passover is celebrated is the beginning of the Jewish year. God decreed it to Moses and Aaron,

Source:

Exodus 12:1-2