Anything for the tank would be helpful, whether it be equipment, additives or even vendor towels. Heck an Alk or Ca pouch from BRS lasts me a few months.
I’d be happy with vendor swag like towels, stickers, shirts. I just recently got the apex so any add ons to that would be great but that’s all super pricey so I wouldn’t expect anything like that haha. BRS gift card maybe?