Might we shop for something other than nonsense?

我们能否购买有意义的物品？

I went shopping for something, but it escapes me what I wanted to buy!

我去买东西了，但我想不起来自己要买什么了！

" To be in the market for (something)" means to be shopping for something, to be considering a certain kind of something that is available for sale; you're deciding which one you're going to buy.

“在市场上买（某物）” 意味着购买某物， 考虑某种可供出售的东西；你在决定你要买哪一个打算买。