Do you have something specific in mind that you would like to donate? Do you have a specific skill you would like to use to help certain causes? Why not create an offer? Causes can then browse through the offers and contact you if they need your services.
For example, if you’re a gardener who has many young saplings and plants that you would like to give away to a retirement home, you can create an offer so that a retirement home can contact you.
Or if you’re a designer and you want to develop a logo for a rhino conservation project, you can put up an offer so a relevant cause can make use of your services.