Dd is also a sugar junkie (takes after mama, ahem). She has very extensive food allergies, so we don't want to take away the sugar altogether--she so rarely gets to "participate" in food with her peers, and she already has so many limitations, that we want her to be able to experience some joy with her food and eat some of the things her peers eat, or allergen-free alternatives.
We simply allow one treat a day, and she gets to pick what and when. So if she wants a piece of dark chocolate after breakfast, fine--but that's it for the rest of the day. She might take a few mini allergen-free cookies in her lunch to school, or if we've baked something allergen-free over the weekend, she can have one of whatever it is when she gets home.
We make exceptions for a few special occasions. If we're visiting relatives for a holiday, and all the cousins are having ice cream for dessert, we won't say even if she's already had, say, a brownie earlier in the day. If it's another kid's birthday at school, her teachers can give her a safe alternative to whatever treat is being offered, even if she had a few cookies in her lunch (we never know ahead of time about these things, and, again, don't want her to feel more left out than she already does). And if it's her birthday, all bets are off!
This works for us. It might not work for every kid and, sure, dd protests now and again, but overall I think it keeps her sugar consumption to a reasonable level while stay letting her feel that she gets enough treats.
ETA: I definitely agree with others on packing a more balanced lunch. That's a lot of grains! Dd typically gets: a sandwich on brown rice bread (turkey and cheese, sunbutter, etc.) OR another protein/whole grain combo (leftover roast chicken and quinoa, for example), plus a veggie (avocado, carrot sticks, cucumber slices), and some fruit. Sometimes she'll get a yogurt and sometimes instead of the veggie we'll put in black beans or lima beans.