Religion is a very complicated matter. There are plenty of religions, faiths, sects. When you see a person, it's quite difficult to say whether he/she is a believer or not, and what kind of confession he/she belongs to. So one should be careful with religious gifts.
The religious holiday number one in the Christian world is Christmas. Nowadays it's one of the most eminent holidays of the year. Traditionally, it's a family holiday. Close relatives and friends give small symbolic gifts to each other. People originated from old-time rich families were swapping presents each of the twelve days between Christmas and Christening. Almost all those classical Christmas gifts - candles, wreaths, bells, pine-tree branches - are not only the souvenirs, but the real religious gifts, which have the certain ceremonial meaning we usually have the least idea of.
Another widely celebrated religious holiday is Easter. People cook or buy cakes and paint eggs. Traditional color of the Easter eggs is supposed to be red. But modern Christians had widened this tradition. Easter is a special day when a simple hen's egg becomes a matter of art. A very wide range of materials can be used while decorating an egg. They are usually presented in small wicker baskets, decorated with some flowers and green branches.
Also gifts are presented on the christening and the communion. The traditional christening gifts are a chain with a small cross, an icon of a baby's saint, a silver spoon 'on the first tooth'. Godmother gives her godchild a christening blanket and a baby's cap with pink bands for a girl and blue for a boy. A christening gift for a mother is a bunch of flowers, but they shouldn't smell too strong not to disturb a child.
The traditional set of the first communion gifts includes crystal and pearl decorated crosses, pictured bibles, rosaries and different keepsakes, like albums and frames with the pictures from the first communion ceremony.
We should remember that the symbols of Christianity like crosses, icons and Bibles should be given to a Christian, or a person who's getting ready to become one. In other cases it may be considered as faith outrage.