I see a lot of videos of people bringing their own slabs to trade with vendors, but is it cool to bring in sealed product? I feel like that might get into a little grey area if you don’t have a vendor table?
To be clear, this would only be to trade with vendors, not walking around with a backpack and a sign.
I saw a guy get ripped apart for pulling around a pull cart of inventory at a show.
If it fits in a backpack or suitcase you will be fine.
Ripped apart by staff or patrons? 
I have been to a few conventions in EU specifically Netherlands and Germany and the only criteria is that in the trading area, you are not allowed to sell for money. This is regardless the type of product you have. I have seen people being called out for having a spread of slabs on the tables in the trading area and just outright selling them with price tags.
Other than that, usually a few people also bring sealed stuff to trade. They also have them on display at the trading areas and you can trade if interested. Nobody seems to have a problem with that.
Cheers!
Other vendors
It’s one thing to bring some items to trade/sell but if you try and be a vendor without paying for a booth that’s scummy. Usually most people have enough sense to know what’s reasonable.
I would use common sense. If you see others trading around tables, then that’s completely fine. But don’t bring cases of sealed product without renting a vendor stall.
Also I think it matters a lot if you’re trading with venders vs the attendees. If you’re goal is to sell to attendees, buy a table. Otherwise it’s fair game