Stony says Matt has 18-inch biceps. Arnold Schwarzenegger's arms were 22 inches at his competitive prime. It's very unlikely that even a large high school student (which Matt clearly isn't) would be so muscular. Stony said his own arms were 4 inches, so he may have been exaggerating.
Before Matt breaks into Dave's room, Dave and Stoney are sitting by the pool, drinking beer, with a keg behind them. After they hear the break-in, the keg and beer glasses are gone, and there is a bowl of tortilla chips on the table. The glasses reappear during the earthquake tremor.
When Dave and Stoney first discover the block of ice Link is frozen in, Dave knocks on it and it makes a hollow noise. However, the block of ice should be completely solid and therefore, not sound hollow.
When Dave's mom asks Link if his necklace is old, Link nods in the affirmative. If Link was a caveman and still had very limited speaking skills, he wouldn't be able to comprehend the question. He also wouldn't comprehend "I'll be back" or "Wheez the Juice," which he saw people do. He could've seen someone nod and mimicked it at (unknowingly) the right time and right place.
The high school-aged characters are seen drinking in a bar and from a keg of beer. Since the reversal of Prohibition, the legal drinking age in California has always been 21. However, no one checks their IDs and it is possible for high school kids to get their hands on alcohol through fake IDs or other means.
The convenience store where Stony and Link stock up on junk food says Food 7 Mart on the exterior shot. Inside, you can clearly see it is a Circle K, most notably, the wall ads for "Thirstbusters" as well as the wallpaper near the ceiling.
During the first scene lots of things fall down during the earthquake, but a full ten seconds after the shaking stops, the ICEE falls. In addition, there is a basketball seen later on the shelf above his bed, which, being round, should have easily fallen down, but is not seen.