A savings bond, or even a symbolic gold chain... provided that the price is reasonably represented in gold weight.
Dowries are/were a symbolic and real proof of financial fortitude, intent. They often a represent real safety net. In some cases, increase the woman (or man's) ability to leave a marriage, a liberty and power balance function.
So much of our modern culture is a corrupt cargo cult. We are completely removed from the meaning behind our symbolisms, both intellectually and culturally.
China's adoption of Christmas and Christmas-like festivities for retail purposes is my favourite example. A copy of a copy with all meaning distilled to "winter shopping."
Anyway... there's no inherent reason for engagement rings, gifts or donations. If we like the traditional/cultural aspects... use them. Otherwise, why so sheep?