Off His Trolley?

I arrived at work this morning to be greeted by my fellow contractor Martin with the words

M. "You didn't want anything from Sainsburys did you?" (He's normally very good at asking if I need anything even though the answer is normally no)
K. "I did actually - I need some mixed leaves to go with my lunch"
M. "Well, I've saved you from having to eat rabbit food then."

So just before lunch, off I went to aforementioned supermarket to buy some mixed leaf (I chose their Italian salad leaves). On the way out there was a man dusting some of the steel framework of the building with a rainbow coloured duster!, I didn't manage to capture that, so instead some of their trollies replacing a man who some might have thought was off his trolley.