I'd keep things simple on the single serving size that people will be ordering with their meal. Upselling sides like a fast food chain does with fries isn't really necessary, and all it will likely do is force you to buy more containers, slow down ordering, and provide one more opportunity for mistakes to be made.
You can still offer different sizes though. Just keep the single serving size at 4 or 6 oz or whatever it is, and then offer bulk containers of say 1/2 pint, pints, and even quart containers that people can take home when feeding the family, etc.
That's how my menu is set up anyway.