As one could guess from the name, candles are a central part of the holiday. In the most simple tradition, they were brought to a church, blessed by the priest there, then taken home to stay lit throughout the night and serve as a ward.
However, we would have a large amount already set about Caerleon as decorations, and they would be lit from the courtyard bonfire blessed by the Archbishop. The feast held after the final candle was ignited consisted mostly of grain-based treats, such as crepes, pancakes, and most other forms of cake.
Those would be the main points... It is not a terribly elaborate holiday. [But any chance to feast is a-okay with her!]