natural resources can be used / combined / played with in any way the child wishes, there is no pre-determined outcome. Heuristic Play allows a child to use their imagination and be creative, without any pressure to produce / achieve something.
I have two variants of this. The 'things from nature' basket which just has shells, wood, stones, feathers etc and 'natural objects' basket including many items from here. This was an easy place to start.