The screwdriver is the clue that helps us infer what Mr. Nitman did as his 'good holiday deed' in the story 'Winter Dreams'.
Step-by-step explanation:
In the story 'Winter Dreams', the clue that helps us infer what Mr. Nitman did as his 'good holiday deed' is the screwdriver. This is because earlier in the story, Mr. Nitman tells Dexter that he helped fix his car with a screwdriver. Mr. Nitman also mentions that he likes to do handyman work in his free time. Therefore, we can infer that his 'good holiday deed' was helping someone by fixing their car with a screwdriver.