I've been a cycle courier (i.e. 'bike messenger') for two years, and vegan for about the same length of time.

I generally try and stick to higher protein food (lentils, beans, chickpeas, brown rice, wholewheat bread, quinoa etc. and fake sausages if I'm desperate) than protein shakes - only because they taste disgusting and they make my sh*t really runny.

Also because I'm not sure if it's a good idea to have protein in such a rapidly absorbable form, on its own - can't be too good for the kidneys...