Are any Buddhist holidays associated with gift giving? If so, which holidays and what types of gifts are customarily given?
In Theravada Buddhism, there are two holidays I can think of that are related to giving: the kathina robe making and the day after the rains is over, called in Thailand devorohana (descending of the lord).
Kathina refers to the frame used to make a robe in the time of the Buddha. After the rains, the monks would gather together cloth they had found or received as a gift and give it to a specific monk; any monk who has a worn or tattered robe is an eligible candidate to receive the kathina robe cloth or, if no such candidate exists, the robe may be given to any monk who is skilled in the making of the robe. Once it is determined who will receive the robe cloth, the community gathers together and offers the cloth. They then have twenty-four hours to complete the making of the robe. If they succeed in the communal effort, the entire community receives certain privileges that last for the next four months.
More information about kathina can be found here.
After the Buddha spent the rains in the Tavatimsa heavenly world teaching the Abhidhamma, he is said to have descended to the city of Samkassa on a mystical staircase. In celebration of this event (and the ending of the rains retreat), a ceremonial alms-giving with a Buddha statue leading the way is often performed on this day, often descending from whatever staircase happens to be handy. E.g.:
Other than that, pretty much all Buddhist holidays (Theravada, anyway) are traditionally seen as occasions for special attention to charity as well as morality and mental development.
Here in Sri Lanka we have Dansal(alms giving stalls) on poya days. Just like how Anathapindika used to do in Buddha's time. Anyone and everyone can come and take as much as they like. I had free ice-cream on last Poson poya day. Usually they give away food items. But recently some have even started giving away phone reloads.