Ideas for inconspicuous material components in prison?

Hello fellow DMs!

I have the age old problem of getting far too much into parts of world building that don't matter that much, so without boring everyone with too much irrelevant backstory I'll keep it short.

A NPC the players have under arrest is a caster that uses material components, and i was thinking of small everyday items he might have scrounged that they can find in his cell. So far I've found "a small straight piece of iron" for hold monster, water for ice knife, "a pinch of lime, water, and earth" for flesh to stone.

I'm looking for things mostly for flavor, and spells one might prepare for contingencies, so i don't care about all the spells that don't have a material component. Thanks! Feel free to tell experiences with using material components in similar situations too