Check out this book: https://en.m.wikipedia.org/wiki/The_Knowledge:_How_to_Rebuild_Our_World_from_Scratch. It analyses that precise question in the first chapter. The author argues that even though Wikipedia is probably the closest thing there is, there is a clear lack of practical knowledge that will be essential in the situation that you are describing. Science progress heavily relies on industrial progress, and even if you know how to build something that doesn't mean that you can do it, as there are other things that are required first.

I am definetly not an expert, but it does look like Chamomile to me. A good test to make sure is to squeeze the flower between your fingers while you smell it. Chamomile has a very characteristic smell, and should be easy to recognise.