1) Half price family nights always go over well, and help to fill seats for games that might not sell out otherwise, then you can make extra money off of them at the concession stands.
2) Throw, pass, kick competitions with local young athletes
3) Fan Appreciation Night - give away team merchandise, autographs, etc. to random seats in the stadium
4) First 15,000 kids get free team t-shirt - if the kids come, their parents do too and you just sold three tickets for every kid you attract.
5) Contest where winner gets to pick 15 - 20 people to watch a game from one of the skyboxes