Chili appears and disappears from the counter after Meat face-plants in his bowl.
When the boys are first outside Porky's and the Sheriff pulls up, a closeup of Porky's face is shown and his cigar is not in his mouth. In the next shot, Porky is in the background and is shown taking his cigar out of his mouth.
Coach Bracket's hair is longer during the "Lassie" scene in the locker room than in the rest of the movie.
After Porky's and the Sheriff's Station have been destroyed, and Porky and the Sheriff have pursued the boys back to Seward County, they are met at the county line by the marching band and various other students, with school buses visible. Because taking revenge on Porky and the Sheriff didn't constitute an official school function, there's no way the students could have come together in this manner. While yes, this may have been done as some kind of "happy ending" thing for the movie itself, Coach Roy was still working for the school at this time (as his dismissal would've been after the semester) and could've gotten students and the marching band together for the celebration. (He did tell Tommy he's "have everything ready" before diving out of the boat and taking off in his car.)
After the destruction of Porky's and the boys drive around by the Sheriff's office, the sign from Porky's is still plainly visible as still being in place. They didn't destroy the sign pointing to where to go to get to Porky's. Only the building itself.
When the boys are weakening the bridge supports with a chainsaw, it's quite obvious that the chainsaw is not running - no smoke, no vibration, no sawdust.
After Tommy comes out of the bedroom at Cherry Forever's house acting as if he was stabbed to death, the door closes over, but not all the way. However, almost immediately after this, the door is closed fully when John Conklin busts through it.
Peewee dials the restaurant on the pay-phone using 8 digits.
According to the guys, Cherry Forever and John Conklin were married. There is no way one could believe an interracial couple would even be living together, much less married, in Florida in the 1950s, even though South Florida is less "southern" than the rest of the state. Furthermore, cohabitation between an interracial couple (married or not) was illegal in Florida until 1964.
The yellow chainsaw used under Porky's club appears to be a Pioneer model 1072 Holiday II. This saw was introduced in 1971 but the movie was set in 1954. In general, chainsaws built in the early 1950's were larger, heavier and too cumbersome for all but the strongest individuals to carry with one hand.
Also, the saw that was tossed into the vehicle as they were escaping was blue, not yellow, commonly used by the Homelite brand.
This movie was set in 1954, but in numerous street scenes more modern "cobrahead" streetlight fixtures are seen. That type of streetlight was first introduced in 1957.
Just before the frame scales down to show the credits, the camera's shadow is visible on the left side of the screen (over Meat).
When Mickey came back to the high school from Porky's after he got his big whupping from him, nobody who looked like any of Porky's goons was behind him when he crashed into the table with the record player and records, hinting that somehow after such a brutal beating he was able to drive all the way back from Porky's and run to the table before collapsing.
A boom mic is visible in the upper right hand corner in the trees of the school parking lot, as Mickey walks forward to ask Billy and Tommy if the plans for Cherry Forever are set for the night.
During the final confrontation, when Porky is threatening the boys with a white bat, he swings the bat slightly and hits his own guy to his right on the nose.