These are the different containers the food is packaged in.
250ml containers are usually for dips and sauces.
500ml are soups or dishes that are served with rice/pasta/potato etc. This size soup is a large bowl full. However, if it is a "topping" i.e massaman curry, it could easily be shared as when you add the rice it becomes a fairly large meal.
1000ml is usually things such as noodle stir-fries, paellas. This size is great for sharing or for those big eaters.
I also do bakes/lasanga in an aluminum tray that can be popped straight in the oven. This is a 20cm by 14cm and 4cm deep. This size container is definitely a shareable size.
For regular customers, I'd really appreciate it if you could keep the plastic containers, which I will pick up when I make a new delivery, so that I can disinfect them and recycle them.