I'm sure it was no big deal, but:
Remember how Jesus said that what the poor widow gave to the temple was better recieved than what the rich man gave (he gave a lot more).
So it's not how much you give, not what you give.
I bet one donut you gave joyfully, from the bottom of your heart might mean more in front of God than Bill Gates giving 1billion dolars for his own publicity.
Food is not a metahore where you quoted it btw, but it doesn't refere to your donuts eighter

It's just that it's very good to make a coustom of giving when you are asked to.
The only instance when it's maybe not the best choice to give is when you know that by giving, you make more harm to the person than good.
For instance when someone asks you mone to buy cigarets or alcohool, you shouldn't give them; but only when they specifically ask for that;
So don't make asumptions to why people need your help/ money / food unless you're certain.
Treat people as you want God to treat you.
If you give something to someone, make sure no one sees you (or as little people see you -- Saint Nicholas (the inspiration for Santa Claus in Estern countries) used to make gifts only at night, buy leaving money when people were asleep so they could not thank him ); do not give so that others will prase you because that will only atract punishment from God (you recieve your payment in this world by being phraised and acknowledged).
Ok, perhaps more than you asked for, but these were things that I was taught by others and I had to tell them to you.