I don't know if they'll have freebies, souvenirs or a food court but what they might have is a Consecrated Host...and no trad should be ignoring that!
Pressure should be put on the proper authorities to cancel this atrocity. Protests have gotten other black masses cancelled in the past.
A few years ago one group was even forced to surrender the Host.
I believe you are speaking about the black mass that took place in OKC. It wasn't the protest that got their attention thereby forcing them to surrender the Host. It was a suit brought against them by the Archdiocese of OKC for stealing what belonged to the Catholic Church (the Host). That particular group bragged about having a consecrated Host in their possession with intent to use it.
I understand the Kansas Catholic Bishops Conference is also looking into pursuing legal action against this latest group, most likely on the same grounds as OKC did (stolen property, i.e. a Host). However, I have not heard or read that this group is in possession of a consecrated Host or any Host at all.
These groups want attention. Protests and petitions only feed their narcissism. Short of legal action (if a case can be made), ignoring them would be the best solution.