My kids are in a school where we're not allowed to bring stuff without permission (too many allergies) and they serve breakfast, lunch, and snack (I love that!) but a couple years ago when my kids were in a different preschool and we had to sign up, I didn't see too many parents other than myself bringing fresh fruit. It was a lot of work, and more expensive than a box of crackers. But, when I'd bring fruit and cheese trays, the kids would GOBBLE it up way faster than the high carb snacks!
One thing to be aware of--moms try to sign up on their kids' birthdays to bring snack. Then we got cupcakes, or in my daughter's case, donuts. She is not into cake. If there are 17 in her class, you might get cupcakes 17 times. You can send her another snack, but it might be hard to resist temptation when the other kids are eating a treat.
We also had to bring a drink. They suggested milk or 100% juice. However, at least two kids couldn't drink regular milk, so a lot of parents were bringing juice. A lot of sugar. I brought bottled water once, but I wondered why they didn't just have them drink from the drinking fountain, or fill cups at it.
I remember one day when I came in with a translucent container filled with watermelon, and the kids saw me outside and yelled, "watermelon! we get watermelon!" They never did that when I brought in the birthday snacks. ;) I would say just set the best example you can. Maybe the other kids will start asking their parents to bring fruit if yours is so good. :)