I generally limit in bike eating to bars, but I see no reason why you couldn't eat a sandwich or fruit. It does how ever come with consequences being less in control and loss of focus on bigger task at hand, how ever if on small residential streets early in the morning that shouldn't be much of a problem. I once was eating an energy bar while mountain biking, and inadvertently steered my self into a rut and lost control and for what ever reason while I was going down my scumbag brain decided I needed to save the bar and not my self so I landed face first with my energy bar well protected with both hands.