The "current" portion of the movie takes place approximately 7-8 years after the "disaster" happened that caused all plant life to die off. If all plant life had died off, there would be no dry grass shooting from the soil, nor dead grass lying on the ground especially with all the weather turmoil happening around. All leaves and dried grass would have decomposed in that amount of time. Furthermore, trees would not have dried leaves hanging from the branches.
The Man is looking for gasoline in an old station but by that point, he'd have already learned that any fuel he might have found would be pretty much useless. Gasoline only has a "shelf life" of about six months. This can be extended by storing it in a vacuum-sealed container but even then, it certainly wouldn't last for years.
In the beginning, the Man is shown to only have two bullets in his revolver. But when we see the front the revolver after he cocked the hammer and pointed the gun at the urinating gangster we see two rounds in the cylinder. The cylinder will rotate again if the hammer is pulled back, so when he fired seconds later the hammer would have hit an empty chamber.