Here are some tips:
1. Practice using the containers you plan to pack lunches in prior to the start of school. Yes, make school lunches and pack them up. Watch how your child handles the choices and how she opens the containers. Are they a source of frustration? Does she know how to open them independently? Independence is the goal--with 20+ children all opening their lunches, and one teacher or a couple of monitors to help, anxiety and temper tantrums are inevitable! Use a visual timer to set the time allowed for eating, then when the timer goes, time is up! Move to an enjoyable activity.
2. Make a list of the things that your child likes to eat and cut them to size. Do you want your child to eat in a particular order? Well, if that is one battle that you don't want to tackle, just pack the healthy things that she eats, and don't worry about order. But, if you do consider the order important, put numbers or symbols on the containers and practise eating in that order.
3. Make sure the drink is easily accessible, as well.
4. Most school have 20-25 minutes eating time, but that also includes dressing for outdoors. Most kids finish eating in under 10 minutes, then need to find something to do. You might pack a little fidget toy in the lunchbox, but keep in mind that might also be a distraction for not eating.
If you practice during the last couple of weeks of summer holidays, snacks and lunch times won't be meltdown times for your child---and your child's teaching team will thank you!