袋子 (dàizi) is a general noun for a 'bag' or 'sack', often made of cloth, plastic, or paper, used to hold or carry things. It is more specific than 包 (bāo), which can also mean 'package' or 'bundle' and is used as a verb ('to wrap'). 口袋 (kǒudai) usually refers to a 'pocket' in clothing or a small bag.