How do you keep long hair, untangled through the day?

I used to have long hair, but cut it during the summer for locks of love. But I'm thinking about growing it back out, another one of the reasons I cut my hair is because i was really tired of tangles. So how do I keep it untangled during the school day? We aren't aloud to have purses so if your suggestion is carry or bring a brush with you, forget it.