To buy items in order to complete or assemble a set of necessary goods (to purchase all items of a series or required items).
入学に備えて文房具を買い揃えた。
I bought all the stationery I needed for starting school.
キッチン用品を買いそろえるのに週末は大型店へ行った。
I went to a big store on the weekend to buy and assemble kitchen items.
撮影用にレンズを買い揃えたいが予算が心配だ。
I want to buy a set of lenses for shooting, but I'm worried about the budget.
シリーズ全巻を買い揃えるコレクターが多い。
Many collectors buy all the volumes in a series.