It never hurts getting some supplies ahead of time for summer times, or indoor pools for that matter, and there can be plenty of interesting stuff in these stores when you mix in magic as well.
Enchanted items abound, one-use rechargeable spells for various purposes, even a few spellbooks on occasion, one of which Aristide's found during his shopping trip and, taking a glance through and testing one of its relatively minor spells just to check it works, it seems like the description might have been a little too vague, or it was a printing error.
Either way, he's definitely getting this one, though going to checkout like this, let alone transporting everything he bought, might be a little bit of an issue. Hopefully they do deliveries, and don't mind bringing him along at the same time.