From what I hear on these boards, back in the day you were able to bring just about whatever the hell you wanted through the stadium gates, but things are different these days.
As far as my stadium (Progressive Field) is concerned, you're allowed to bring binoculars, cameras, and signs. When it comes to food and beverage, you are not allowed to bring in bottled pop, but juice boxes and pouches are OK. You can also bring sandwiches, peanuts, chips, and other small snackable items.
Oh, and of course, you cannot bring in your own alcohol or any sort of weapon. I hear that they don't like laser pointers either.
Here is something interesting though: With the exception of the last game I went to, they always searched the bags you brought in and gazed into purses, sometimes even patting you down. As a matter of fact, we had been caught trying to sneak in pop a couple of times. However, the last game I went to, they didn't check a single thing and I walked in with a bag full of stuff. I wonder if it is because attendance is so bad that they can't afford to turn anyone away.
Anyway, what about your stadium? I'm sure it varies and I wonder if there are any peculiar things that are allowed or not allowed at your stadium. Also, do they go out of their way to search you too?