The only things we could salvage were a couple of mints that were wrapped in cellophane. = The only things that we could salvage were a couple of mints that were wrapped in cellophane.划线部分是两个定语从句。前一个从句修饰的先行词是 things，其中的 that 在从句中作 could salvage 的宾语，可以省略；后一个从句修饰的先行词是 mints，其中的 that 在从句中作 could salvage 的主语，不可以省略。

    could salvage 是 can salvage 的过去时形式。