Navratri is celebrated to worship goddess Durga also known as Annapurna: The one who feeds people. Annapurna is the one who will provide for the hungry, whenever there is a need.
Being a part of Annakshetra, it has been a different experience of Navratri since the last few years when on one hand, Langar, Bhandaras and Jagrata are organised to seek blessings of the Goddess so that no one goes hungry, while on the other food is wasted in the form of surplus. Food is cooked without any forecasting, calculation or an estimation of the confirmed guests/participants for any given event.
Religiously, it is preached not to waste Prasadam (blessing of god), but surplus prasad collection in huge quantities at Annakshetra is an eye opener. One valid reason that was prominent through my experience in the field is that calculation for the quantity of food is proportionate to the contribution made by community to support religious activities. Fact remains that contribution/donation are made as donation, faith and devotion, but not to consume the cooked food. The donor of food usually buys coupons for prasadam, which are more in number than the family members. The idea is to extend support to the kitchens in various religious establishments.
Having these lack of knowledge about the number of attendees and feeling of faith and devotion, the organiser remains in fix when it comes to deciding upon the quantity of food to be cooked. They will have to keep preparation considering contribution, assuming all those will turn up and if less is made, there remains a possibility of shortages if all contributors turn up.
Perhaps, Goddess Durga will be happier and give blessings if all the food that had been cooked is utilized to feed someone, and does not just end in a dumpster.
Annakshetra has a suggestion to implement: Ask for actual number of people attending the feast at the time of seeking contribution/donation; and as attendees, make sure you communicate the number of people accompanying you for the feast well before the date of the event.
Once again to recapitulate: Goal of Annakshetra is to achieve ZERO FOOD WASTE not to increase number of food recovery and redistribution.