WRap there feet in a wet paper towel this will help prevent freeze drying.If there is blood from the bill gebtly open ther mouth and insert a cotton ball this will catch any blood that may secreet during the freezing process.
gentley tuck there head under there wing & double wrap them in a non porous bag such as a bread bag or large zipper bags if there small. a wal-mart bag or grocery bag is an example of a poruos type.
store them in a deep freezer below 0 degrees
do not store them in a un heated garage or out side during the winter.
if they are not below zero they will still slowly be able to decompose .
so the colder the better!!