I have used WD-40 to get out grease stains. It loosens the grease from the fibers. Coke will also get out a lot of stains.
I have had good luck using the Tide to go stain stick pens to get out tomato stains. Not sure why it works, but it does.
If you can't buy oxyclean, you can make it. Just google how to make oxyclean or oxiclean.