If you want to implement something like this, I recommend you take a rule from AD&D. If the character makes the save, all items are unharmed (or minimally harmed), but if the character fails, then the items can be damaged.
In AD&D, items had their own saving throws, but for 5E, I'd suggest items follow the normal AC and HP for items. If a character fails the save, then some number of random items are damaged (such as 1d6-2 items) , taking some percentage of the total damage (I'd suggest 10% to 25%, otherwise very few items will survive any AoE). Damaged items can be repaired, unless they're broken (0 HP).
In AD&D, items had their own saving throws, but for 5E, I'd suggest items follow the normal AC and HP for items. If a character fails the save, then some number of random items are damaged (such as 1d6-2 items) , taking some percentage of the total damage (I'd suggest 10% to 25%, otherwise very few items will survive any AoE). Damaged items can be repaired, unless they're broken (0 HP).