I understood that the events occured this order described below. (１)：Your grandmother had given you the blanket in the other day. (２)：You brought it and said "Good thing I brought～." →良い物を持ってきました、祖母がくれた毛布ですよ。 ​───────追記​─────── Chii-sanさんの方が正確です。 Chii-sanさん、ありがとうございます。 The URL below is to reference that. 【Good thing ....】 https://american-phrases.blogspot.com/2014/06/good-thing.html?m=1

I think, for example situation, the speaker bring oneself the blanket in a course of a trip, and when the speaker is under low temperature, she/he found the blanket and said, "よかった！おばあちゃんがくれた毛布を持って来ていて。(Good thing I brought the blanket my grandma gave me)". *my grandma = 祖母/おばあちゃん *Good thing = It's a good thing = …してよかった ※Ayumiさん、どういたしまして。