The practice is free to attend, and the parking is free as well. There are concession stands that sell food, drinks, and beer. Be prepared to pay normal stadium prices for food and beverages, however, if you buy it there. In past years parking has been in lot 22 along the west side of the stadium and it's a short walk over to the fields.
Along the west side of the stadium has also been the Patriots Experience, filled with interactive games that allow fans to test their kicking, passing, and tackling skills on a variety of obstacle courses, football tosses, and other similar challenges. It's a popular draw for kids. And while you're in the area, you may also want to check out the stores and restaurants at the ever-expanding Patriot Place or combine a trip to Training Camp with a visit to the Hall at Patriot Place, which is an absolute must for Pats fans. (For a good, cheap meal, I highly recommend Five Guys Burgers at Patriot Place.)