Common issues are bulbs, tire inflation, tire wear, shock performance, and alignment.

Personally, with an old (2006, 200-300K km) car that we had to NCT every year, we would pass about half the time on the first time, and half of the failures were for BS reasons (e.g., one of the removable seats wasn't installed, it was in storage, or a tent peg dropped into one of the 3rd row seats when they opened it, and couldn't close it again).

Even with that NCT, when winter rolls around, 5-10% of cars have obviously broken headlights on any given dog walk.