You should place your plastic containers outside to catch sunlight whenever you can.  In everyday use, wash them in hot water and rinse them with white vinegar (let the vinegar sit for a few minutes and then wash again with dish soap and water).
The good old baking soda is always a great help. To remove stains, mix baking soda with warm water and apply this paste to your plastic containers. Leave it overnight, and you’ll see the results.