The symbols and tools of the modern Fianna are taken from the myths and legends. They are the tools and symbols of various persons in the stories and just as symbols should, represent the Fianna as a whole very well.
The Spear: The spear is a truly multifunctional tool. At first thought it is representative of Lugh's spear, but it is also the weapon commonly used by the Fianna and Celtic warriors of that era. In a modern context is can function as both a spear and staff, representing the war/peace duality that I can see the Fianna being placed within.
The Crane Bag: The Crane Bag is symbolic of both Fion and Mannanan Mac Lir. It is the personal "identity" and ritual bag of the Fiannaman. It contains those items which represent the Fiannaman and could be used by the Fianna during devotionals away from a primary ritual site. These are very personal and the items within need not be shared with others.
Other items may include a shield, chain shirt, a set of clothing consistent with what was worn in the period of the ancient Fianna. I myself would use these items as "ritual" clothing and would wear them when attending any kind of outdoor Pagan festival. If wearing "traditional" dress, the warrior caste wore 3 colors. I think it appropriate to continue this practice.