A Big Gulp cup is thrown near the cop, which disappears in another shot.
In between shots of Stevie's group and the cop show Fourth Grade either filming with his camera or not.
The same chartreuse yellow colored van passes in two different shots.
(around 24 min.) One passing automobile disappears in between shots of Stevie and the cop.
The M-branded skateboard that Ray offers to Stevie is right side up, yet in one shot - the board's facing upside down.
"Tenants" is misspelled as "Tennants" on the sign behind the skate shop.
The Sony Handycam used by Fourth Grade (Ryder McLaughlin) is a CCD-TRV16 camcorder. This model was released in 1998 and if this film precisely took place either in '93, '94, '95 or '96 (hence the Mid90s title); this would mean this camcorder model is anachronistic being manufactured as early as 1998.
The film is said to take place in 1996 yet Stevie and his brother play PlayStation (1) with dual analog controllers. The first PlayStation launched with a D-pad controller with no analog sticks; dual analog controllers didn't release until April 1997 in Japan and late August 1997 in the United Sates.
When Stevie and his friends are shown skating down the middle of the street a 2003-2011 black Lincoln Town Car is clearly seen driving towards the camera. Later in the film they are shown skating down the same street and this time the modern Lincoln is driving away from the camera.
While Stevie and his friends skate on a two-way street, a modern Toyota Camry passes by in the background. Likewise, an older Lincoln Town Car passes on the road as Stevie skates along.
When Stevie hurries into a nearby bathroom to sanitize himself, the AmPm store clearly has a modern logo.
When Sunburn falls through the gap and is bleeding, his skater friends remove his shirt he's using as a rag to stop the bleeding, putting Ruben's shirt on because Sunburn's got too covered in blood. When using cloth to stop bleeding, new cloths should always go over the old ones, as removing the old one gets rid of the pressure that's needed to stop the bleeding (possibly deliberate since the skate punks likely don't have this knowledge).