Security precautions at government and public buildings now may require you to show a photo ID to enter to use the restrooms, water, or pass through there grounds.
Carry at least enough change to make a phone call (if there are indeed pay phones on the route). I think it wise to take a couple of dollars (or your national equivalent) just in case you want to buy a snack or drink or other small item. Even if just walking around the neighborhood, you may run across a child's lemonade stand or a rummage sale.
On the other hand, many of my friends make their walking pay for itself by collecting recyclable cans and finding spare change on the street as they walk.
Carry your identification and money in a zippered pocket of your clothing or pack, and check once in awhile to make sure the zipper is closed.
