I picked up a Smokepowder Satchel that says it explodes when ignited, damaging everything in the vicinity. Some enemy spells can inflict burning. Will a Smokepowder Satchel explode if a character gets lit on fire while carrying it in their inventory?
Nope.
Your inventory is safe from the environment, and vice versa.
That said, a lit grenade is probably not the best thing to store in your pack, even if you're the only one who's going to suffer for it. But even in such a case, the rest of your items (smokepowder satchels included) are fine.
