I found a lot of different answers online. But according to five different sources, every NFL game is equipped with 24 footballs. (Plus, I remember reading that in a recent Sports Illustrated.)

According to the NFL Rules Digest, "The home club shall have 36 balls for outdoor games and 24 for indoor games available for testing with a pressure gauge by the referee two hours prior to the starting time of the game to meet with League requirements. Twelve (12) new footballs, sealed in a special box and shipped by the manufacturer, will be opened in the officials鈥?locker room two hours prior to the starting time of the game. These balls are to be specially marked with the letter "k" and used exclusively for the kicking game."

I heard 30 balls

maybe somewhere from 5-10 (just a guess!)

i think around 32.