We met my son GF over a Zoom call. So there’s that… Your son has to realize that just dropping by with nothing to do to meet the GF can be awkward. Having a meal or as you stated something by the fireplace sounds great but also kinda set up. I personally like a traditional meal, lunch/dinner and if they want to they can come early to help cook and set the table to break the ice or something like that. This strategy has gone well with both my son and daughter friends. I would not worry about the conversations. Let them happen organically like you would with anyone else. There’s enough going on in the world and I am sure she has parents, siblings you can ask about or some major/job she’s doing. I wouldn’t touch politics but you can ask your son ahead of time about topics you might be curious about. I hope your son has told you something about her.
The last BF was met over sushi at the kitchen counter. Very relaxed. It only has to be awkward if you make it that way. Treat it like meeting any other of your kid’s friends.
I don’t really think you need to plan anything, IMHO. I’ve observed both ends of the spectrum.
When I introduced my significant other to my parents, we just kinda hung out in the living room and chatted a bit with the TV on in the background. Even again a few times after that, same thing. It wasn’t till a few months later that we did any actual activity with them - we went to a food truck festival and a car museum.
When he introduced me to his parents, it was the opposite First his dad visited to help him with his car when it broke, and then insisted on taking us out to dinner that night, so I met him then. The first time I met his mother was a month or two later… we drove 5 hours north to visit. It was kind of funny - He got laid off and I suggested that since he didn’t have to work, he could take a few days and go visit his mom while job hunting. (his dad was elsewhere working on selling their house). He then responds with “oh, ok. what days would you like to go?” I’m like… Oh. Guess I’m going with. She then planned all these activities - we had to go to multiple museums. We didn’t sit around a tv at all, and we went out to all these restaurants. It’s usually similar each time we’ve visited since. I think she wants to make the most of each visit with activities since they don’t see each other very often.
never mind, missed the shared hobby bit… reply cancelled
I find the whole planning a bit creepy and awkward. I would just put out something like Veggies and hummus, chips and guac. Just ask how their drive was and let the conversation naturally flow. Some of the suggestions on this thread seem like an adult play date. To each their own.
I’ve noticed that some people are generally more anxious than an average person and planning helps them control their anxiety levels. OP sounds anxious about making a bad first impression on someone who can very well become a part of their family in future.
Prior GF asked to see albums of son as a youth, then we watched a video.
i think it wouldn’t be awkward if we had already met gf in some sort of organic, fleeting way – we live in the same city, we see our son every so often for the usual assortment of things. I had suggested exactly the same things that have been suggested, (hey, bring GF when you come to help stack wood, pick up your skis, etc) this was rebuffed. Son relates that her previous bf reveal went poorly and helped end the relationship, so now she (and maybe he) feels wary? I agree it feels overthought, but I am just staying in my lane. It won’t make her less nervous if I am fussing about details.
They haven’t told us a date, so it is still possible they’ll give up this too-formal idea and just pop over unannounced. It’s also possible the schedule won’t work out at all and the whole thing is scrapped. Trying to not have opinions about why we haven’t met her long ago, but apparently earlier than 6-8 months is rushing. Oy.
Let us know how it goes - when it comes!!! 
It seems your your son or his girlfriend are feeling insecure and your non intrusive but supportive behavior is just the right amount of help needed at this point.
How about going for a hike? This allows for some pretty unstructured time – one-on-one with Mom and her or Dad and her. Avoid the 20 questions interview that I got from my future FIL.
Then, hot cider or cappuccino or something nice after the hike.
We meet her next week! Oooo the suspense 
Let us know how it goes and what y’all end up doing!
This is turning into quite a love story with whole CC community waiting in suspense.
ta-daaaaaaaa!!
They arrived as I was putting the pizza in the oven, son helped DH start the fire and I stuck my head out of the kitchen to yell hello. before we ate, talked about the shared nerdy hobby.
Chatting about photos in the living room, stories about tree ornaments, pizza’s done, we sit to eat. GFand DH have some professional overlap so they talked shop and then she talked about her newly accepted job offer. pizzas done, son wisely says let’s go burn more things.
back poking the fire, more q & a (about her siblings’ locations, it came up) interview horror stories, convo about an event they are going to tomorrow. I told her a bit about our families in the course of things since I assume she might have questions she is too polite to ask.
I said, at 2.5 hrs, maybe you need to get home to check the cat and you’ve a long day ahead, they got organized, I kissed my son, hugged her, DH waved.
Literally 2 minutes after they leave, my DiL texts me “are they gone? what do you think? is she a keeper? TELL ME EVERYTHING”
Don’t keep us in suspense, we have all those questions too! 
I hope your son was satisfied and enjoyed the time too!
Pizza and a fire- perfect.
Sounds great. You will look back and laugh about you overthinking the whole thing, I have experience in that!
Your family sounds like a thoughtful and welcoming bunch. I’ m glad it went well.