It might seem indulgent to buy lots of different plastic boxes, but given the importance of choosing the right box, it is worthwhile to do so. Daiso and Lock n Lock provide good selections at affordable prices. Wherever possible, choose airtight boxes as they will prevent spillage of any sauce or liquid contents (I’ve packed soups and yoghurt before), while also keeping dry foods like biscuits crisp in humid weather.
Beside the main lunchbox, I also have a selection of other plastic boxes: smaller ones for pieces of cut fruit (which accompany every meal bento I have), a round box for a single muffin, a deep, rectangular box for two muffins, and shallow rectangular boxes for angular snacks like pieces of cake. Most of my plastic boxes are not reserved for bento use only as we use them for storing all sorts of foods at home, such as dried goods removed from plastic packaging or leftovers in the fridge/freezer. With a large variety of plastic boxes on hand, I can easily find one to suit anything I want to pack into my bento bag.
Aside from boxes, I regularly carry a small insulated mug/flask, and always have a wet towel (oshibori) and plastic cutlery –either a fork and spoon in a ziploc bag or foldable chopsticks which come in their own case.
You’ll need a bag to hold all these things. Again, it’s good to have bags in different sizes to accommodate the amount of food you’ll need. The bags I use most of the time hold my lunch, fruit and a snack. I also have one larger bag, which can also fit a one litre water bottle, and several smaller zipper or drawstring bags from Daiso which hold a single plastic box and cutlery and sometimes also an oshibori. Usually, the small zipper/drawstring bag will go inside my main holdall or backpack, where it helps to keep the food items together and hopefully, prevent the food boxes from being knocked open as well.
If you do mostly rice bento rather than sandwiches, it’s much better to find a bag that will allow you to hold the bento boxes horizontally. Briefcase-style lunchbags tilt your boxes on their side and may disturb the arrangement of food or increase the chance of spillage. It’s not necessary to go hunting for dedicated lunch bags, any small tote bag with a large enough flat base will do, although I am very partial to two-layer bags that enable easy access to the main lunchbox itself.