Cue Card Warm-Ups

Lately I've taken to using the back of Cue Cards for quick practice sketching.
I find it easier to be loose and carefree while sketching on them as they are so disposable I'm not afraid of turning out a bad picture.

Here are some quick studies I did using Google 'street view' as my reference. (I recommend this to anyone wanting to practice buildings etc) As well as one sketch of my lovely girl working away.
I tried to spend as little time as possible on each card.