Vinegar works for wool and synthetics, but consider spot-testing in an inconspicuous area first.
Hydrogen peroxide is color safe and also disinfects, making it great for removing blood or rust stains.
Rubbing alcohol is effective for removing inks, dyes, and chemical-based stains.
Dish soap works to clean clothes of grease stains, helps remove oil stains, as well as stains from condiments when mixed with water.
Mineral spirits and acetone can be used to remove paint stains but can be harsh if used on synthetics.