In high school I knew a kid who would go around looting loose change from unlocked cars. He'd pull the driver side door open like it was his car, hop in, loot the center console, then hop out like nothing happened. He wouldn't take valuables (as far as I knew), just change, so maybe a few bucks per car.

His rationale? "Nobody will cry over a few missing quarters and they are free to lock their doors anyway."