Happy sack is a colloquial term for a bag or backpack that is carried with a sense of happiness or contentment. There are several synonyms for this term that express the same happy and positive connotation. Some of these synonyms include joy bag, bliss bag, delight pack, cheer sack, and merriment carry-all. Each of these terms can be used to describe a bag that is carried with a feeling of joy and satisfaction, and are perfect for use in casual conversation or creative writing. Overall, these synonyms evoke a sense of positivity and happiness, making them great to use in any setting or situation.