Agreed. The skills to utilise found materials are always with you. That's true in wilderness and in cities. Both environments are awash in resources if you know what to do with them.

To that end, I always carry gear that helps me improvise -- in essence, tools that help me create the tools I need.

A practical example (under $30): when travelling by air with only carry-on luggage, I always carry a double-sided diamond sharpener. Security looks at it, but has never hassled me. I know from experience that I can always borrow or scrounge a used kitchen knife or pruning shears at my destination. And, I have practised operating with them so I know what they can (and cannot) do. But I guarantee you that they will not have a working edge. Out comes the diamond ...