Donating money to the temple
Another way is that family & friends collect money and put it in the "money tree" and at the day of donating one person of the family will give it to the monks.
This is they way it did happen with some friends of us. My wife had made donating coins (wrapped in strings like a flower) and we did put some money in an envelop for donation to the temple. On the day of donation we did visit our friends and helped them to put all the money on the tree. The big notes (500 & 1000 Thai baht) in the top and the smaller notes (100, 50 and 20 Thai baht) a bit lower of course.