Mabon is the Autumnal Equinox. This year it is September 22 for the northern hemisphere. Mabon is the pagan Thanksgiving. It is a feast to celebrate and share the second harvest.
Usually the second harvest is the most plentiful. Lammas is the first harvest and is a feast on the early fruits and vegetables. Samhain is the last harvest and is a feast of the last late crops. Mabon is also the Autumn Equinox when night and day are equal, after this date our days begin to get shorter and the nights get longer. During Mabon it is a time to make offerings to the trees, these are usually ciders and juices, the peels from any fruits and veggies you eat at the feast. As pagans, us witches love our feasts, but it is important to remember to share what the God and Goddess have provided your family with. Sharing with friends and family is our way of saying thanks! This is a time to collect seeds for the next year.
Breads, nuts, apples, and root vegetables are all symbols of Mabon. Decorating your personal altar with these is a beautiful way to celebrate the season changes. You can find a ritual for Mabon here. I don't have a solitary ritual because I feel that Thanksgiving should be celebrated with others! It is a time to see the leaves changing and feel the chill of winter peeking around the corner. Now would be a good time as well to provide the squirrels with acorns and other nuts and dried fruits for winter. For this celebration I like to gather pine cones with my kids and make the classic pine cone bird feeders with peanut butter and bird seed. You tie a ribbon to it, coat it heavily with peanut butter (or yogurt if there are allergies it just doesn't stick so well) and then roll them in bird seed pressing down to get a good thick layer. Then you hang them in trees or around your yard for the birds.