My view is that if you're the only journalist being offered the sandwich tray, avoid it. But if every journalist covering a large event is being offered the same, go eat if that's convenient and helps you make your deadline.

For example, when reviewing pop, rock and country performers for the Winnipeg Free Press, I would often be offered, during times when I was backstage obtaining some background info prior to a show, to help myself from the always impressive spreads the promoters had had to provides for the bands as part of their performance contract riders. I always refused politely, as it was something only being offered to me. The fact that I had already eaten before going to cover an evening show wasn't really a factor. From time to time though, I did see colleagues from the Winnipeg Tribune indulge. Perhaps that's one of the reasons that paper folded. lol

But at large events, from Canadian or U.S. national political conventions to international conferences in foreign cities, if there was food and drink provided freely and equitably to all accredited media, I would indulge if it helped me do me job and allowed me to meet deadlines. (i.e. avoid long lines on-site or long treks through security barriers to obtain food)

If a selection of somewhat stale tomato and lettuce or egg salad sandwiches on white bread (Kyoto Conference Centre) or Anchor Steam Beer and all you can eat steamie hot dogs (Moscone Convention Centre in San Francisco, courtesy of the American Federation of Railways at a national political nomination convention), to name just two examples, influenced what anyone covered or reported, I'd be amazed. Though that Anchor Steam Beer was pretty good. lol

I think they mean that the sandwiches on the sandwich tray are not to be eaten on practical rather than ethical grounds -- been handled through. It's like the food at a church potluck -- eat at your own risk.:)
In a small community paper you'd cause more offense than it is worth than to turn down supper at these events, and in any event, if you are doing your job at a small community paper everyone knows you are going to write whatever you want anyway. You've already established that by offending everyone in power locally at least once. As was mentioned, these events are also chances to network and have people tell you about potential stories you didn't know about.
Finally, I don't know how many reporters have told me free food should be avoided on ethical grounds, but will openly talk biased political opinions to anyone who will listen. Or they will take awards and the money that comes with awards from groups and organizations that are not run by journalists. That is far more troubling as a source of perceived bias than food.
On the other hand, if you work for one of the Toronto English-language dailies, the bias of your newspaper is already well established, so what is the point of turning down food, awards, etc.?

Well, Duncan, just for starters, the uncouth ink-stained hacks have a bad habit of handling all the sandwiches in search of the chicken salad . . .

Okay, so I'll agree that the sandwich tray is verboten. But what about the rubber chicken circuit?

When I started out in journalism, back in the Pleistocene Age, the assignment editor would send you out at least once a week to the Rotary or Lions Club lunch to do a story on what the "featured speaker" had to say. You'd find an opening at a table, make amiable conversation (networking), and eat a plate of rubber chicken and overcooked vegetables. The understanding was, no quid pro quo. Rotary didn't even get a plug. But their speaker got a few lines on page 6. ("Economic future uncertain, says local banker.") Back then, it seemed both practical and good social manners. What's the protocol today?
1) Arrive after the lunch, listen to the speech, and leave.
2) Have lunch, but pay for it.
3) Call the speaker later in the day, and get a copy of his speech.
4) Ignore the event altogether.
5) Eat the damn chicken, and remind yourself that you can't be bought by a lousy meal.

If you have a reputation that you can be bribed into a biased story by a free lunch, then things are pretty bad.:) While I think there are probably times when free lunch should be passed on, I think your blanket rule is way too strict. You may well cause more damage by causing offence in some cases. Going out for lunch may be one thing, but what about covering events where they give the media free food and everyone else pays? Not just the rubber chicken awards circuit -- sports writers and photographers are routinely fed and fed very well at high level sporting events. (The Detroit Tigers at one time were renowned for the food they had on hand for the media.) Does Toronto Star policy forbid the writers and photogs from chowing down?

Why wouldn't you eat off of the sandwich tray?