There's some that I started many years ago and forgot about completely.
The thing is that I"m getting low on panels so I've been going through old paintings considering painting over them.
Anyway, I just had 151 panels cut from some 1/4inch baltic birch plywood. I spent a few days sanding it smooth (My shoulder is now paining me). As soon as the weather gets nice I'll seal them and put a few layers of traditional gesso on the front. This process takes several days but the finished product results in the most exquisite painting surface. Silky smooth and perfect for applying egg tempera. Here's what 151 baltic birch panels looks like:
151 panels should last me about a year. Plus I do the odd large painting on stretched canvas.