The UK government set aside £40m for Afghan aid
An investigation by a panel of MPs said "banditry and lawlessness" following the fall of the Taleban had made it difficult to deliver food to all those who need it.
And much of the $720m (about £500m) pledged to Afghanistan since 11 September by donor nations has not been turned into hard cash, the report found.
Prime Minister Tony Blair has stressed the importance of a humanitarian coalition working alongside the military action in Afghanistan.
But the Commons' International Development Select Committee report said: "The collapse of the Taleban did not bring the safe humanitarian space which had been hoped for, it often substituted one security concern for another. Banditry and lawlessness replaced military conflict.
"The primary distribution of food has, despite all obstacles, been delivered in adequate quantities, but the failure of secondary distribution systems has prevented its delivery to all those in need.
"Secondary distribution has been inadequate because of the lack of security over large parts of Afghanistan."
Drops could resume
The committee said aid workers should have "greater protection" under international law.
And it said that if security could not be established in Afghanistan, airdrops would have to be
considered as a way of delivering aid - but as a "last resort" only.
Committee chairman Tony Baldry, Tory MP for Banbury, said: "We are very critical of dropping food parcels, peanut butter, from planes. It is a pretty daft thing, particularly in an area full of landmines and other ordnance.
"There have been occasions when the UN has resorted to, effectively, air lifting and dropping food. It is very much a last resort."
The UK has put aside about £40m for humanitarian assistance to Afghanistan since 11 September - about half of which has already been allocated.
It has also announced £11m for short-term support to neighbouring Pakistan, and £15m to support the government of Pakistan in its continuing reforms.
But despite donor pledges, six million people in Afghanistan are facing a food crisis, and the World Food Programme predicts 14% of the vulnerable population will be hard to reach in the winter.
'Deafening silence'
The report called on the United Nations to review the "fragile" way its humanitarian operations are funded.
It also called for the international community to stop forgetting about various humanitarian crises throughout the world.
The committee said although refugee camps in Pakistan have been there for nearly 30 years, they had been abandoned by the international community in the mid-1990s.
And Mr Baldry said there had been a "deafening silence" on the Afghanistan humanitarian situation before 11 September.
"We have to try to ensure there are no forgotten crises of this kind," he said.