Well, at least here in the Philippines. Actually when I eat from the tray, I intend to make it easier for the busboy to clean up the mess because the mess is all on the tray (yes, we have busboys here at fast-food joints - a luxury, I'd say). The busboy would just have to pick up the tray to clean up the table. In the States, where there are no busboys at fast-food restaurants there, almost all diners eat from the tray. Afterwards, they dutifully take their tray and throw their mess at the garbage bin and place the plastic tray in its rightful place, leaving the table clean enough for the next diner. And thereby eliminating what would've been a busboy's dirty work.
It's not even a cultural thing for American diners. It's more of simple table courtesy - if you make a mess at your table, clean it up. Or prevent the mess altogether and heap everything on the tray. Here in Philippines fast-food joints, we're not accustomed to cleaning after ourselves. We just get up and leave wrappers and leftovers for the next diners to see and sometimes, even have to clean up for themselves. Okay, so that's how it's always been and who am I to criticize culture? But personally I hope we would at least be mindful enough of the busboy or the next diner. It would be well-mannered and chivalrous to see someone clean up after themselves, despite the availability of an overworked, underpaid busboy. I'm pretty sure the busboy wouldn't make fun of me if he saw me eating from a tray. In fact, I'm sure he wouldn't mind at all.
Another thing that strikes me is the fact that we have baggers at grocery counters at many supermarkets. Yes, it's a simple and decent job, to bag groceries at the check-out counter, and I respect the industrious people at that job. But in other countries, there is just one cashier and no bagger in sight. Beside the cashier, there is a metal tray-like holder with two hooks to hold up the plastic grocery bag, while the cashier puts the groceries in the bag after the goods go through the price scanner. The metal contraption for the grocery bags is very simple - nothing hi-tech at all; it just hooks and holds - but it eliminates what would have been a bagger's tiresome job of grabbing and dumping each good one by one. Whew!
Okay, before a labor union shoots me down, let me emphasize that I'm not advocating the elimination of busboys and baggers. What I mean is that common courtesy and thinking out of the box could push us to develop our labor skills further. Admittedly, I think many of our jobs and job practices are still backward and other jobs are even obsolete already. If we're going to develop as a country, I think it starts with competent, skilled labor to serve the changing needs that science, technology, industrialization and globalization bring us.
It may start with fast-food tables, grocery counters or wherever. As soon as we ourselves initiate change, that's the only time we can expect change in return.