If I'm out in the wilderness and I don't have a signal mirror, what other objects could I improvise to work similar to a signal mirror?
It sounds obvious, but check that you haven't got anything like a sighting compass on you or anything else with a mirror - I once heard of someone who was rescued but the process was more difficult because of his lack of a mirror. Later investigation found he was carrying such a sighting compass the whole time!
If you really haven't, then find the shiniest thing you do have that might reflect light - a glossy notebook, glasses, transparent base of a comapss, anything like that. It won't be as good but it'll be something at least.
Of course the other option is to light a signal fire with lots of smoke if you can - burning damp foliage is the classic option here.
I think someone may have mentioned a knife being an emergency kit essential item. Well, here is one great reason: A knife can be used as an improvised signal mirror.
From today's news: Three Lost in Oregon Use Knife as Signal.
I try never to go out into the woods without a good knife. I now have one more reason to never leave it back at home.