Over the holidays I made some baguettes, but unfortunately forgot to pick up polenta (i.e. coarse cornmeal) from the store while I bought ingredients. The polenta keeps the dough from sticking to the pizza peel (or back of baking tray) while it rises. It makes it a lot easier to slide into a hot oven!!!
I also think polenta gives the bread really great flavor. It's even better with pizza crusts. Try it next time you make a crusty loaf of bread! (I'll post a recipe at some point.)
We scrounged through the pantry to find suitable replacements, and after trying to quickly make bread crumbs, considering oatmeal, and even looking at some Malt-o-Meal (before realizing it was brown sugar flavored), I realized that popcorn might work.
We used D's dad's coffee grinder to grind up some kernels (I wouldn't do this on a regular basis--it kind of wears on the grinder), and voila--coarse cornmeal.
What are some of your substitution tricks?