When Mud and Gaby are in the bus, they are talking about growing up and dating. In the front shots Mud is laying back in his bean bag, but in the reverse angle shots, he is sitting upright on the edge of the bean bag.
When Zack is making the necklace with that one girl, the other girl comes in and stands behind him. Her sleeve is pulled over her right hand and not the left, yet when the screen switches to another shot, her sleeves are reversed, covering her left hand instead
Towards the beginning, when the kids are throwing their stuff into the fire. One of the kids, suggest, that Steve, throw in his cello. For the first few minutes in the shot it's standing up against the burning logs. In the next shot when they are are yelling "nowhere", you get a glimpse of the fire, and the cello, appears to be gone. It's impossible for the cello and case to burn that quickly.
When Zack tries to buy beer, the cashier states that you have to 19 year old to purchase it. The film takes place in Pennsylvania. The legal age to purchase alcohol in Pennslyvania has been 21 since the end of prohibition (1933). Furthermore, they purchase beer in a supermarket. In 1994, PA did not allow the sale of beer in grocery stores and supermarkets.