As an HGV driver I could tell you of lots of things other drivers do whilst behind the wheel of a car or van, some of those things are much less savoury than one would like to imagine at this time of the morning!
Motorway plod have trucks without speed limiters that pull alongside and video what you are doing whilst driving. This includes, obviously, usung a mobile phone, eating, fiddling with anything that might be construed as illegal.
On cycling, I find it awkward eating as it affects my breathing so tend not to.