Imagine that planet Earth had a sister planet, like our Earth, but without any people. 
Imagine that you could magically transport humans and all their possessions to this planet, one at a time.
How many people would you need to transport to create a standard of living equal to our Earth?

Without a period of rebuilding knowledge and capital, I believe that the answer would be quite close to seven billion.
Virtually all of humankind is integrated into a global web of civilization. The physical and mental bonds linking every human being together are just as essential to our survival as our technical knowledge and capital assets. 
A humble billboard by the highway requires many relationships between the property owner leasing his land, the media company that paid for it, the construction company that builds it, the company that paid for the ads, and many more.

The economic ecosystem is self-healing, and individual gaps are often rapidly filled. However, greater damage takes longer to repair, and economic recessions which destroy a larger part of the economy can take years or decades to recover from.

According to most science fiction, the answer to my question might be a few dozen. In fact, we have no idea what the “minimum viable civilization” is at current levels of the standard of living – but I suspect it’s in the order of hundreds of millions of people.

A “civilization bootstrap kit” might be possible one day, but even a complete set of our formal knowledge and technology would only contain a fraction of complexity that makes modern life possible.

“There is the question of how our knowledge really does arise. Most knowledge – and I confess it took me some time to recognise this – is obtained not from immediate experience or observation, but in the continuous process of sifting a learnt tradition, which requires individual recognition and following of moral traditions that are not justifiable in terms of the canons of traditional theories of rationality.”
– Friedrich Hayek “The Fatal Conceit: The Errors of Socialism”