"Regarding prasadam, leftovers should always be taken if they have not spoiled or if they have not been touched by diseased persons. We should never waste Krishna prasadam. Best thing is to cook only what is required and then give each person what he wants. That is the Vedic system, that the people sit in rows behind their plates and servers pass down the rows and put a very small portion of each foodstuff on each plate, unless there is some objection by a person then nothing is given. Then if anyone wants more, the servers pass up and down the rows continually and give more if anyone requests. In this way nothing is wasted and everyone is satisfied."
Srila Prabhupada Letter to Kirtiraja, 11-27-71
"No, food which has been offered should never be put back into the refrigerator with the unoffered foods, or brought back into the kitchen. You should prepare as much as can be consumed, and after offering, nothing should be put back in the refrigerator, or kitchen. Refrigerator should always be very cleansed and pure. Everyone should be careful to make only as much as they can eat; they cannot keep any leftovers in refrigerator. I know this is a practice in your country, but in the temples or at homes of any Krishna Consciousness persons, a person should not indulge in such unclean habits. If there is any food extra, that should be kept separately; and if there is a separate refrigerator, not within the kitchen and not having in it any unoffered foods, then you may have such special refrigerator for leftover prasadam. But it cannot be kept within the same refrigerator as the unoffered, unprepared foods. That cannot be."
Srila Prabhupada Letter to Aniruddha, 06-16-68
"The eating area must be thoroughly cleansed with water, since the area has become impure by the act of eating. One thing is that you should keep everything very clean. That is the first business. Every room should be as clean as a mirror. The prasadam room should be immediately cleaned after taking prasadam, otherwise you are inviting rats."
Srila Prabhupada Letter to Mukunda, 10-20-73
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.
At the temple or at large feasts, servers usually collect all the plates and utensils at once. In small settings, however, one should dispose of their own plate when the meal is finished, or wash it outside of the kitchen. Afterwards, one should wash the hands and rinse the mouth.
One should not sleep, bathe or engage in strenuous activity directly after a meal. Being over-active may cause the blood to flow away from the stomach to other areas, thus interrupting the digestion process. After taking prasada, one should maintain a peaceful mind so the body can properly digest and process the nourishment. This time is well spent remembering the Lord, chanting His Name and discussing the Lord's pastimes with associates.