Some thoughts from yesterday's life drawing session:
First of all, charcoal is a great tool. Seriously, it's pure joy - I haven't tried it for ages and almost forgot what fun can it be. I don't know how to describe it properly to give you the right picture - but imagine that you think you can't make tone even darker for it's already RGB(0,0,0), and then you still apply few additional strokes, pressing the stick so hard to the paper that it begins to crumble, and yes, you receive the darker colour every time. Feels like magic.
The second thing is, that because of the charcoal features you find yourself no longer afraid of large formats and empty white sheets which usually scare you away when you are with your pencils only. The volumes and spaces can be toned with the charcoal in a moment, so it doesn't take long to fill all your medium.
And thirdly, the large formats that become possible to cope with proper tools available are surprisingly much more convenient when it comes to proportions which is important in life drawing. When you look at your picture from some distance and when the unavoidable aberrations in the hand-drawn line are not significant comparing to line's thickness and length, things become easier.
Resume - small formats and notebooks are good for urban sketching only. When you have an opportunity, take the A1 or at least A2 - even if the result is not so different in your case, the fun surely will be.