Examples of things that could be considered treasure by garbage gnomes: Broken/old computer desks, broken/old computer monitors, used/old stained mattresses(because surely those stains could be removed), broken/old furniture, broken/old televisions.
*Garbage Gnome drives by and sees said garbage*
Garbage Gnome: I can't believe someone threw that away!
*Garbage Gnome loads up something from the garbage in their car/truck/suv*
*Kelly wakes up in the morning, walks outside and notices the recliner she threw out missing*
Kelly: Well, I hope they manage to fix the broken arm on that recliner that grand dad used to piss in while watching tv.