Druids as with most peoples celebrate certain festivals, and even today we continue with these human traditions. Everyone loves a festival or celebration and all are rooted in either thanksgiving for what has been or hope for the future and what is to come. Some revolve around special events which have spiritual or cultural relevance.
The beginning of a season or time of harvest has long been remembered the world over, as has the end of an year and the beginning of a new one. The moon and sun played a big part in many basic civilisations but as knowledge increased and an understanding of science and spiritual truth grew the celebrations changed to match that awakening.
Most of the celebrations attributed to Druids come from a mismatch of sources, a lot from the 17th Century revival and the neo-druids which have no purpose other than an excuse to do something to excess. Historic celebrations are generally founded in actual climatic changes, witnessed and experienced by people which had good or bad outcomes on those people. This is why we see historically a lot of cultures trying to change future outcomes through annual practices.
An agricultural based culture usually has seasonal celebrations and the Druids do celebrate these along with some others that have other more spiritual meaning. Most if not all of the celebrations were and are of thanksgiving in nature they were never designed to offer up payment to deities to change the future, Druids were well aware of who and what controlled the universe and their part in the great mystery of life.
Today many of our traditions and celebrations are based on consumerism, which is the base of the culture today, we have lost site of the bigger picture and have become seekers of goods or fun rather than knowledge or enlightenment. We look forward to Boxing day sales and Black Friday sales, Summer holidays and weekend breaks, the things which take us from our lives not connect us to life.
Sadly a lot of the original festivals have been lost over time as Druids were an oral culture, but we see (for those who know where to look) in the origins of the Druidic culture some of those lost festivals or traditions. Just like today the festival, celebration or tradition, whatever you want to call it does not define the person, you can not say I am a whatever because I do this and that. A lot of what makes a Druids is in what they believe and think, what they do and how they live.