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Does "change of clothes" imply that..
1) You need more than one set of clothes (at least two shirts, two pants, and two underwears), OR
2) That you need an extra shirt and pants and underwear (two or more items)?

To put it in another perspective, say you read the below email:

"Change of clothes... That's all you need! We'll leave Thursday night and drive back Sunday eve.... We should be home Monday morning."

How many pants, underwear and shirt will you bring?
[NOTE: Do not let the other part of the quote affect your judgement]

1) 1
2) 2+
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I do agree that the phrase "change of clothes" would normally imply only one extra set, but there's no way I leave on Thursday and return on Monday and then wear the same thing Friday, Saturday, and Sunday. So you might have to expand your definition a bit in this case!
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"Change of clothes... That's all you need!"

This says nothing about the number of changes of clothing required– it is the uncountable form of 'change'.
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Comments  
Personally, I read that to mean I should bring the clothing I am wearing, plus one extra set.
 BarbaraPA's reply was promoted to an answer.
 Mister Micawber's reply was promoted to an answer.
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