According to the EPA, Americans throw away over 12 million tons of textiles a year; more than 85 percent of that eventually goes to landfill. Synthetic materials take years to biodegrade. Nylon takes 30 to 40 years; polyester over 200 years. Consignment stores do not always accept rejected clothes, so it's best to divide your clothes between old gym T-shirts that no one will wear and your label items that are in good condition.
For the "consignment" bag, Thred-Up is an excellent option if you are strapped for time. They send a bag to fill with your sellable goodies (excellent condition and recognizable labels) and you get paid once sold on-site. If you are not looking for compensation, nonprofits such as Dress for Success and Career Gear accept gently used clothes to help people get back on their feet. You can also reuse your online shipping boxes through Give Back Box which is a convenient and hassle-free way to donate to charities.
Now for the "recycle bag" of worn gym leggings and your dad’s ripped jeans that somehow turned up in your wardrobe. Madewell has a program that turns preloved jeans into housing insulation for communities in need—and gives you $20 off new ones. Organizations such as Grow NYC, USAgain, and Planet Aid recycle unwanted textiles, turning them into wiping rags, stuffing in cars, or insulation.