(around 1 hr. and 22 min.) When Donny and Mary McGarricle are fingering on the glass, the top of the boom mic momentarily enters the shot. As turns out, this is actually the microphone from the TV crew.
Todd tells Donny, he can't come down to the until he puts on a tie. Donny says he hasn't worn a tie since his mom's funeral when he was 3 but in the court room seen young Donny is wearing a tie for the trial.
In the scene after Grandma finds all of the tissues on Donny's bed, Todd goes into the bathroom to wash his hands. When Todd comes out of the bathroom, the light is on, but when Donny says the line about "La Vida Loca," the light is off.
When everyone is visiting the church, we see Chad in his USMC uniform with the correct PFC rank insignia on his sleeves. For a brief second he is seen with a Corporal's insignia which switches back to PFC in the next shot.
The goof item below may give away important plot points.
Incorrectly regarded as goofs
In the scene when Chad comes home, he is wearing Marpat Desert Cammies without name tags and his PFC chevrons are upside down. The character is later revealed to be an impostor who isn't a member of the Marines or any other branch of the armed services, it's natural that he would not be aware that he was wearing these things incorrectly.