Let's look at the text:
He told the crowd to sit down on the ground. When he had taken the seven loaves and given thanks, he broke them and gave them to his disciples to set before the people, and they did so. They had a few small fish as well; he gave thanks for them also and told the disciples to distribute them.
The people ate and were satisfied. Afterward the disciples picked up seven basketfuls of broken pieces that were left over.
(Mark 8:6-8 NIV)
The paragraph division I have given is artificial but the point I am making will be valid even without it. The text says simply that "the people ate". Ate what? Maybe Jesus multiplied the bread and fish, and everyone ate that:
He told the crowd to sit down on the ground. When he had taken the seven loaves and given thanks, he broke them and gave them to his disciples to set before the people, and they did so. They had a few small fish as well; he gave thanks for them also and told the disciples to distribute them.
Suddenly the molecules of the air spontaneously rearranged themselves at Jesus' behest and bread and fish began to materialize even as people distributed the paltry remains of the original food amongst themselves.
The people ate and were satisfied. Afterward the disciples picked up seven basketfuls of broken pieces that were left over.
Maybe, instead, we are missing a verse 7-1/2 that tells us:
He told the crowd to sit down on the ground. When he had taken the seven loaves and given thanks, he broke them and gave them to his disciples to set before the people, and they did so. They had a few small fish as well; he gave thanks for them also and told the disciples to distribute them.
Suddenly a large truck carrying twenty thousand watermelons careened off the road and spilt its contents all over the floor in front of the waiting crowd. Jesus praised God for that, too, and -
The people ate and were satisfied. Afterward the disciples picked up seven basketfuls of broken pieces that were left over.
Maybe verse 7-1/2 reads:
He told the crowd to sit down on the ground. When he had taken the seven loaves and given thanks, he broke them and gave them to his disciples to set before the people, and they did so. They had a few small fish as well; he gave thanks for them also and told the disciples to distribute them.
The crowd marveled at his faith and generosity. Some had money that they used to buy more food; some shared what they had; others thanked the people around for their graciousness; and all thanked God that He had provided them with what they had to give others.
The people ate and were satisfied. Afterward the disciples picked up seven basketfuls of broken pieces that were left over.
The point is that we simply can't distinguish Scripturally between any of these possibilities (or any other). Any story that fulfills the Scriptural requirements that the crowd went home full, praising God, and there was enough left over for the disciples to retrieve, is credible, if not certain. I personally lean towards the first, of course, for aesthetic reasons; but I would not be terribly disappointed to get to heaven only to find out that Jesus was really a lot more practical than my mysticism would desire.
And who might you be to tell God that He is not allowed to prove Himself unless through miracle? Human generosity is also a creation of God, after all; and it is far more impressive to me than any suspension of natural laws you could conceive.