Would be interested to know the answer… I always take a bus on the rare occasions I make it to a game, mostly because I’m not sure what to do with my helmet (and bag, although I can leave that at home and just take a lock)
I’ve had people bring full briefcase-sized messenger bags in although I think they can refuse to allow it. The security folks seem to be pretty nice (though I go to a lot of games so maybe they trust me). At the playoffs the NHL gets more involved so typically they get a little more rigorous. And this goes for Pens games only, concerts are probably different.
There’s not a lot of room in the seats so I’d limit your cargo.
The seats are definitely tight, but when I go I usually get tickets from a friend who has seats in the last row. It has the advantage of having a ledge between the back of the seat and the wall where you can put stuff. It’s way farther from the ice than the last row of E in the Igloo though (although you can see the scoreboard…)