I've lately been in the habit of visiting the V & A with a little A5 spiral-bound sketchpad, which is a no-brainer of an accessory as it's very easy to carry around and use and (more importantly) most of my sketches are done in A5 size anyway. Most of the time I carry around A4 paper and do a picture on half of it and then struggle to find a use for the other half of the page.
Above are some busts from the V & A's collection. Having received a set of lead pencils for Christmas, I've pushed the boat out and tried using those for sketching instead of my usual soft grey colouring pencils, and am pleasantly surprised to find that the results haven't been completely disastrous. The nicest find has been the really extreme "B" pencils like 5B and 6B, which push the drawing into levels of darkness I've previously only been able to achieve in post using tonal correction in paint programs.
The down side is that lead pencils, especially the dark ones, smudge very easily, and a couple of really satisfying pictures have fallen victim to the dreaded grey mist as a result of spending too long in the drawings folder in my bag while waiting to be finished.