OK here are some tips that I do from time to time to get extra food as a poor fuck (excuse my writing).
Now if you are ordering on a party or some kind of gathering pizza or anything else order a menu from a restaurant or something like that. For example 2 pizzas here are like 25-30$ but if I order a Jumbo pizza with 20 pancakes and 1 cheeseburger and 3 0.25l sodas i get it for just like 20$. This is good to do just before the closing time because they throw in all the shit that they made extra so that it doesn't go into garbage.
The next thing is not sure how it is in you country but here the Red Cross is lazy as fuck so when the restaurants have a lot of extra food they usually throw it (rarely keep it especially if they are high start hotels/restaurants) or call the Red Cross to come pick it up. Now these lazy asswipes want everything handed to them so they won't come for it and the restaurant or hotel just throws it into the garbage.
So I sometimes call these few restaurants and say that I volunteer for a student group that helps out the poor ones or smth like that and ask if I can come pick up the leftovers. This works great and after some time they even started calling me to pick it up so I had to much and actually would give it away to some homeless ppl on the street.
The next thing is also useful but it depends on your luck. If your buying some sandwiches from a restaurant go there to pick it up right before the closing time and you just might get the food that didn't get picked up. Worked for me in like 6 out of 10 cases it also helps if you are a regular and good with the waiter or waitress.
And the last one you can always crash a wedding ninja mode and eat for free and drink.
Hope this helps some of you.
Also feel free to post some other methods.