In the scenes shot around the "Port Sunshine" pub you see local Scotrail electric trains running past, (the actual pub is in Clydebank), but they have dubbed the sound of high speed express diesel trains.
It is frequently mentioned that the events of this film take place 20 years after the events in the original movie. Renton states that he is now 46 years old. There is a flashback to the characters as children, and it is explicitly stated in the end credits that the characters are all 9 years old. Therefore, Sick Boy would surely know that 20 years ago when Tommy died, Tommy was nearer to 26 years of age, not "22 or 23".
Spud and Renton both state that Renton left Spud £4,000 at the end of Trainspotting. "His share." If you go back and watch Trainspotting the money is in £2,000 bundles. Renton only leaves 1 bundle in the box at the airport.
In Sick Boy's flat Renton and himself are talking about George Best when he played for Hibernian Football Club. When they slide on the pitch it is Tynecastle Park which is home to Heart of Midlothian, not Hibernian.
In the original movie, Mark puts up half of the £4K required to purchase the Russian skag from Mikey Forrester, so he would only owe the other 3 a share of £8k from the £16k sale (the proportion of the "4 way split" of the haul wasn't specified in the original).
The goof item below may give away important plot points.
It is obvious that in real life, the Police would have rushed immediately to Begbie's wife place after his escape, at least to check if he had been in contact and if not would have kept a surveillance daily.