Lammas (also known as Lughnassadh in honor of Lugh) is a modern day neo-Pagan festival in honor of the harvest and the harvesting of the first fruits. It is celebrated every August 1st and is associated with grain, corn, apples, and grapes.
As a Hellenist, integrating Lammas into my modern worship is fairly straightforward. The first deity who comes to mind at honoring, celebrating, and offering up of “first fruits” is obviously Hestia, the goddess of the hearth and home, and the intermediary between us and the gods. She assists with the gods’ receiving of offerings and is the go-between. She is always honored both first and last in offerings to the gods as a result. The next god is clearly Apollo, a deity who has quite a bit in common with Lugh including his association with agriculture, the sun, skills and arts. On a complete UPG (unverified personal gnosis) note, a Celtic seer once told me that she saw Lugh all around me, and I knew she was looking at Apollo. Whether or not this means that Apollo is literally Lugh or she was simply looking at my gods through a Celtic lens does not matter, but syncretism is certainly a very valid belief and an ancient Greek one at that. Therefore I genuinely feel that Apollo is an extremely valid choice on this day to honor him. Demeter is another good choice to honor on Lammas day, as both mother of Persephone and goddess of grain and the harvest.
This is the time for gratitude for the harvests in your own life, for celebrating all that you have reaped so far in your life. It is also the time to prepare for the coming of autumn as the sun begins to wane in strength and the days grow shorter and colder. I myself ironically have a company party on this day to celebrate our new and way better office location, and given how much I absolutely love and am thankful for my job, the timing could not be more appropriate.
As far as magic is concerned, this is also a good time for prosperity and protection magic.
On this day, let us give thanks to Hestia, she who without whom the gods cannot be honored and made due offerings, to Apollo for agriculture and sunlight, and to Demeter for the grain and the harvest.
Hail Hestia! Praise Apollo! Praise Demeter! All hail!