In addition, I suggest a hat, sturdy footwear, layers of outerwear that can be added or removed as conditions warrant, and a compact umbrella for unexpected rain. Sunscreen and insect repellent are also useful to have on hand. I never leave home without a water bottle and a snack!
All of these items can be stored in a grab-and-go daypack, or in the trunk of your car (except binoculars, which should be stored at room temperature), so that you always have them on hand.
photo © adrian binns