Had one of my long posts typed out. Decided to shorten it, so this is the short version!
Do not burden yourself with things you don't want, like or use, even if they are useful -- if you haven't used something in 5 years or see yourself using it, you are just storing potential and how useful is it really??
For truly bad fabric, like that which runs, we have fabric recycling which is where things like old pillows also go. Don't pass on problems!
For other stuff, plenty of ways to donate. Small amounts can go to a thrift store. It will do best if you fold it neatly and put it in a clear bag/large ziplock baggie. Large amounts can go in boxes, but make sure the store will take them that way. In my part of the country, pretty much all general thrift stores (as opposed to clothing consignment) have fabric in the linen section.
Pretty much every Tuesday at my weekly small group someone is offering fabric "before it goes away". Is funny the different things people want, couple weeks ago I had a bag of stuff I had gotten at the thrift store and one of the ladies was just thrilled by a piece of vinyl in there for a machine cover she wanted to make for her son or something... People are always giving us bits of fabric and such as well. We support several different charity groups ourselves (either with fabric or projects) and then pack up the non-quilting stuff and donate it back out.
We all have different tastes, different budgets, and not all of us are quilters and some are happy to use poly blends. Even those that are might want to make a project to take to the beach or for a horse or whatever....