Help people locate places to donate their stuff and they'll be less likely to simply toss it. There are a lot of places throughout SF other than Goodwill & the Salvation Army to donate things. There are freestanding donation bins on a lot of corners, churches that seek donations, food banks, charities that seek donations, etc. A lot of people toss things (food, diapers, toiletries, etc.) because they don't know they can be donated.