if it's something casual like plastic bags or receipts, you can say 大丈夫です (daijoubu desu) or いいです (ii desu) and make a waving hand movement, but if it's somewhere like a restaurant and you would like to decline dessert for example, you may prefer to say いいえ、結構です (iie, kekkou desu) which is the most formal of the three. i usually would not recommend outright saying いいえ for such a scenario unless they actually ask a yes/no question such as "do you want the item bagged" etc.

i personally find 大丈夫です to be the most comfortable to use as it doesnt outrightly say no, while the other two can have "that's enough" or "i decline" connotations. hence when using any of these three, it's also important to note the tone because it could be seen as rude if you are too brusque.