Well then why didn't the 5 wise virgins share their oil with the 5 foolish virgins? And doesn't the Bible say, "Each one must carry his own load"?
Seriously, though, if someone was too poor to bring their own meal, they are probably too poor to travel to the convention site anyway. (Except for local homeless people who might wander in looking for a free meal.) Usually those with special needs - elderly, single moms, etc - are either brought there by someone else (who can feed them) or receive financial help through their congregation so that they can attend. For example, a single mom "in good standing", the congregation might pay for her gas money, motel room and meals.
Myself, if I was too poor to afford to bring my own lunch (let's say if I had lost my job or something) I would not merely show up and hope to receive a handout. I'd make arrangements beforehand...ask for help from a friend or from the congregation.
Another thought. Why should the publsihers bring extra food to feed other attendees? Let the society set up an arrangement for them. They can add it to the cost of having the convention there, and recoup it from the contributions.