Do you compost? That's the first suggestion I'm finding, but I don't garden so that wouldn't be a useful suggestion for me.
If the boxes have been opened, I don't know what org will take them, but if you have sealed containers, local food pantries will grab them. If there's a local buy nothing group, you might find takers even with open boxes. If you work in an office or group setting, you could give it away. If there's a local group like a church that has meetings with tea or coffee, you could possibly be like "i have a million boxes of stuff I'm not using" but they might be like other orgs and not want to take open boxes.
Some towns will have special recycling times for stuff like that. Biowaste, I think it's called?