Hooray for good neighbors that can help you in a pinch, but when that fails, a Real Mom will now be equipped in what to use as a substitute:
Substitute for 1 egg
2 Tbs flour
2 Tbs water
1/2 Tbs oil
1/2 tsp baking powder
Put this in your dough in place of the egg, and continue on in your awesomeness. Works like a charm in almost all recipes (except of course omlettes, scrambled eggs, etc. You catch my drift).
Now speaking of making cookies, I've got to go get mine out of the oven. Yes, egg-free.