May mornings can be cold and windy. Pack gloves and a warm hat, even in early June. If it's warmer, a baseball-type cap can keep the sun out of your eyes, which is immensely helpful for locating bird movement. In spring and certainly in winter, warm clothing layers are critical. Synthetic underwear and either wool or fleece layers are best, especially beneath rain gear on chilly morning.
Cotton kills when wet in winter.
On most outings sturdy boots are preferable to tennis shoes. During summertime outings, muted, loose-fitting clothing works best. This stuff is cool and great for insect protection. We usually don't have to fight insects. Folks who are sensitive to mosquitoes and black flies can pack repellent or wear long sleeves and pants in muted colors and perhaps a bandana around the neck.