Jonah collects.  He likes the process of collecting.  He likes to walk around with multiple items in his hands, preferably small and colorful things that he is not allowed to touch.  We came across these beautiful seeds the other day on a walk and between the two of us we came back with quite a few:

And as mentioned in the interview with Michaella Ruffino, Jonah likes bottlecaps as well:

Below is the toddler equivalent of a nature collection:  nature bracelets!  I put a piece of masking tape around each boy's wrist (sticky side out) and they could stick on bits of flowers and leaves as we walked. 

Jonah's is above and Benjamin's is below.