The barley loaves were food for the poor. In our time, they would have been stale bread. Philo refered to barley products "suited for irrational animals and people in unhappy circumstances".* And these loaves were brought forward by a very small boy. Wouldn't you agree with me that with a crowd of 5,000 men, not to mention the women and children, there would at least be quite a number of them who brought food? But they were unwilling to give them away, lest they have none. It took a small little boy with very menial food to do it. Imagine how would it be if those with better food would have offered theirs instead. The food multiplied could have been much better.
In the same way, what are we giving to God that he can multiply? Things we don't need? Our "spare" time? Our loose change?
*Well, I suppose we could misinterpret Philo in our contemporary times, especially with what we do with barley!