Let them make it.
Your kids are going to have to eat it, so once they're old enough, let them make it. Establish rules about what they're allowed to have and approve each menu in advance. Make it part of your routine and lead by example (just make sure you follow the same rules).
If they aren't old enough to actually pack their own lunches, get them involved anyway. They'll learn that it's part of their responsibilities early on. Plus, they'll be more excited about lunch if they have a say in what they're getting.
Start the night before.
Put as much together as you can the night before. If you're sending leftovers, store them in the container(s) you'll be sending. If you're worried some ingredients may not last if they're mixed the night before, do as much as you can. For example, put the meat and cheese on the bread in one container. Put any pre-prepped veggies in another. Put it all together in the morning in a few seconds.
Prep like a sous chef.
In professional kitchens, they do as much as they can to knock off valuable time later. You can do the same at home.
Buy plastic ramekins with lids and prepare several individual servings of commonly used condiments (mustard, mayo, dressing, etc). These items keep well, so they'll be fine individually, too.
That's not the only thing you can make ahead. Boil several eggs as a quick add-on for salad (or as extra protein on the go). Cut and pre-bag veggies (such as carrots), so you can grab them quickly. When you cook dinner, make a bit extra of certain ingredients or dishes for use later in the week.
Create a lunch-packing zone.
Set aside a space in your kitchen and refrigerator for lunch-packing. Buy cheap plastic containers in various sizes for quick packing options; that way, if the little ones lose them, you can replace them easily. Store plastic bags, prepackaged options and other handy items here.
Chill a little.
No morning will ever be perfect, no matter how much you plan. Some mornings, you'll just have to give your kids money for pizza in the cafeteria. Cut yourself some slack.
More back-to-school food ideas
Best after-school snacks for busy families
Ways to keep kids full longer
5 Tips to get kids cookin' in the kitchen