I would not use "useless". The paragraph specifies that the things are still in working order. You could use "used".
Interested in Language
It's me for the last time tonight.
People in The Netherlands have come up with a simple alternative to throwing things away -- the "goedzak," or "good bag" -- a half-transparent plastic bag people can use for setting things that are still in working order out on the sidewalk for others to collect. Designstudio Waarmakers, the company responsible for creating the "goedzak," says that "design for altruism" was the inspiration for the gift bags and not necessarily sustainability.
In my opinion, " for others to collect" refers to useless / unneeded items that are placed in half-transparent bags on the street.
I'm not sure what you're asking. The "others" are passersby who might want the thrown-away items.