They tend not to- in my experience, at any rate. More ritualistic spells sometimes require a channel... whether that be something somewhat magical in nature itself, like a wand, or something textual like runes...

[It was admittedly something she'd studied a bit, and she got to thinking, leaning back into the chair cushion.]

There are also items that have been given power previously, either by the mage using them or another... runestones, power gems, the like...

[How to categorize these...]

And some are just tools used to give form to a spell... like a crystal ball, a scrying pool...