Vinegared Food, Pickled Food
noun
A vinegar thing is a thing that has been vinegared. This is a vinegared food or a pickled food.
すのもの
The readings are the readings for 酢 and the kun'yomi reading for 物 which you've seen quite a bit by now.
大人になったら酢の物が好きになりました。
She came to like pickled food as she grew up.