Most of it's already been said, but:
A clean, empty spray bottle and an eyedropper can be invaluable under the right conditions.
Cornstarch is great for stopping bleeding.
Vetricyn is a good wound wash.
Epsom salts are good for a lot of things.
A big sock can be good for restraining a bird's wings to its side. I had to stitch up the back of a Mallard's upper back once (no idea what happened. It was a clean cut) and I had no one to hold him for me. So I cut a hole in the end of one of my Dad's old socks and shoved him down in there. Opened it up enough to reach his back, made sure he couldn't grab it with his feet, and it worked like a charm.
If you raise/hatch chicks, a heating pad might be a good investment. I hate getting up in the middle of the night to make sure the hot water bottle's still hot.