I work with a non profit riding camp as well and we love donations. It's amazing what different programs want and it's always good to ask what they'd like.
Surprisingly our biggest wants, people don't always think about. More brushes, reins, headstalls in all sizes, throatlatches (kids always seem to lose these to the mud) and various bits. We go through great trouble trying to find the perfect bit for each horse and it's great when different ones are donated so that we have a variety to pick from.
How great of you to think about donating your equipment.