Over the years I have packed a lot of lunches and I have found that lunch bags with a shape similar to the one above are the most useful and adaptable. Other shapes are often too small and not as adaptable when you want to send a food flask with leftovers along. We got ours from John Lewis and they have been going strong for the past 3 years. These bags are washable and can even be put in the washing machine for a jolly good clean.
The next essentials to have are lots of little leak proof plastic boxes with clip lids. These make sure that nothing you send can leak into the lunch bag and are reusable so you don't waste money on foil and plastic. They also mean that you can make your own single serving version of things people like to eat, rather than playing inflated prices for a manufacturer's version.
Finally, a food flask with a wide mouth, around the 1/2 litre, will fit into the lunch bag and keep the leftovers you send piping hot and so avoiding food poisoning ! The food flasks vary in efficiency and I would thoroughly recommend looking for reviews before purchasing them. We have some Thermos ones which are alright for keeping your morning cup of tea hot but by lunch time the food is cold. Whereas the Stanley ones are amazing and will keep your food hot for up to 12 hours, really good if you are travelling !
Do you have favourite equipment for packing lunches ?