I have been reading "Grimm's Fairy Tales", and have come across the term "had his goose with him". In one story, the character "did not have his goose with him", and as a result, was light enough to be flung into the air by a branch as it sprung up. In another story, the character "thanked God that he had his goose with him" which prevented him from being blown out of a tree. Although carrying a literal goose with you, could increase your weight, it wouldn't be by that much, and it didn't make sense in either story for the character to be carrying an actual goose with them.
Do you know what this phrase means?