For Networking Lunch, I don’t think you need to bring the membership card (if I am not wrong… ’cause I never go for this event). And you can bring your guest(s) along since we are just paying for what we order. It would be better if you could clarify with the Networking SIG Coordinator though.

For Soapbox, you will need to register via the link with your Mensa Account once the link is opened. So far, they have never asked me to present my membership card though when I do the registration before entering the room.
The talk is free for all members & you can bring a guest along for free. Subsequent guest(s) have to pay $5 each at the event itself.

For Cocktails & Calories, you don’t have to bring your card. You can bring guest(s) along as well. Same theory as the Networking Lunch.

For Chill & Chat (Board Gaming Session), you do need to bring your card along for verification.
At the counter of Settler’s Cafe, there will be a clipboard whereby you will have to fill in your Name, Membership No., Signature & the Name(s) of your Guest(s) before joining the games. You do NOT need to register online for this event.
Same as the Soapbox Event, you can bring along 1 guest for free. However, subsequent guest(s) will have to pay $7.50 each instead.