When Jake meets the mysterious girl in the museum, he is wearing a gray suit with a dark pink tie. He's still wearing that suit on the train, but when he arrives home, he is wearing a dark suit with a red tie.
When Jake and Davis are in the car before the wedding, Davis tosses his cigarette out of the car. He then immediately has a lit, half-smoked cigarette in his hand.
When Kristy tells Jake she stopped taking the pill, he is shown on a rocket sled which crashes into a concrete wall. When it explodes the size of the flame doesn't match the size of the wreckage - it's clearly a model. However, it can be dismissed as being part of Jake's imagination.
In the Club scene early in the film, you see Jake holding a bottle of beer while he and the Club Girl are baking eyes to each other. He's drinking an empty bottle.
When Jake kisses his wife goodbye, comes down the sidewalk, stumbles, and falls, a blue pad to protect his knees is clearly visible on the sidewalk.