It's a matter of choice as it's been said. But uf you're going to spend the money on good supplies, you'll probably want to keep it acid/lignin free as much as possible. For example, acid free adhesive--why use otherwise when it's readily available and does make a difference. Likewise paper. You know newspaper yellows and degrades fairly rapidly so it's better to photocopy or scan it. Or if I really want to incorporate the original, I'll spray with a sealer rather than a de-acidifier. I'll never use a pvc plastic since it de-gasses, nor plant materials like real flowers, or rusty metal. I'll probably not use leather either,( avoid heavily alkaline stuff also). But fabric and ribbons?--sure--ubless it's acetate! Buttons? Yup. They don't say acid-free but I know it's okay.
If I know something is acidic, I'll avoid it. (Most inkjet transparencies are made in an acid bath, for example.) If I can find a readily available alternative I use it. If I have to use something and I'm not sure, then I probably will use it...unless I suspect it's going to degrade or cause other stuff to degrade.