I am in my yearly quest in San Francisco for the perfect hot cross bun. One poster had never heard of them and this seemed better on the General Board.
The hot cross bun is traced to Pagan Spring festivals in honor of the goddess 'Eastre' ... like Easter. Even the ancient Greeks had a bun similar to this dedicated to their own group of gods.
As the excellent link below on the history of the hot cross bun says "The shape of the bun was said to represent the moon whilst the four quarters divided on the top of the bun represented the four quarters of the year."
There are a lot of superstitions about the bun. Like with many Christmas traditions, the Catholics took over the pagan celebrations giving them their own spin. So this bun was served during lent, the cross symbolic of Christ. It seems it always has been a symbol of spring and rebirth.
The article below talks about other pagan spring rites and symbols (bunnies and eggs).
The pretzel actually has it's origins in the Catholic Church. Early Lenten practices prohibited eating eggs, milk or fat, so bread during Lent was made only with flour, water and salt. The shape was supposed to represent arms crossed in pray.
Here's a more detailed history of the pretzel link.