Side to serve with tuna noodle cassarole a la Mad Men?

Thanks for the great suggestions! Sam, I was planning on a slivered almond and Parmesan topping but i will try your fried onion suggestion too.

Sorry, didn't mean to suggest Ants as a side... just as an appetizer. I think the post above that suggests Creamed Anything has it right. It was common to have two or more creamed dishes at one meal.

Ants On A Log, though it's more of an app than a side. You could "dinner" it up by adding a hotter spice to the cream cheese or swirling in some chutney with spices. Maybe exchanging sliced olives for raisins.
Finishing touch would be TV trays and those compartmentalized foil TV dinner trays as dishes. And maybe hire a snippy 11-year-old to make the drinks, like Sally?

Waldorf salad?

And please put either fried onion, or crushed saltines on top of the casserole...I know you said low carb..but use some a TNCassrole, needs some crunchy topping. You could just make some onion sliced very thin dusted in corn starch and fried to crip. A minor carb--and extra texture.

Ceasar Salad. Good yeast rolls and soft butter. Appetizer: Classic Shrimp Cocktail in Martini Glasses. Desert: Baked Alaska.

creamed anything!

Or cucumber cups--little hollowed out sections of cucumber filled with a savory mixture.

I luuuuv spaghetti squash...It's so hard to find it in Brazil,I haven't had it for years!But enough about me;I think a three beans salad would be a good match.

Classic iceberg wedge salad, layered salads...also, I recall my mother often making 'green beans almondine' for dinner parties in the '60's (basically steamed/parboiled fresh green beans, sauteed in butter/oil with sliced or slivered almonds and s&p) - still fairly popular, but I think it was more of a 'thing' in the '60's.

Dream Boats! Avocado halves surrounded by watercress and cherry tomatoes and dressed with a red wine vinaigrette.

My Sunset Menu Cook Book from the mid 60s has several things like:
the Athenian Green Salad (iceberg, butter & romaine lettuces, avocado, tomato, feta, olives, anchovies and a simple red wine vinaigrette)
Apple & Avocado (butter lettuce, watercress, apple, avocado, olive oil, white wine vin., tarragon and walnuts)
Mixed greens, mandarin oranges and dressing of oil, oj, orange peel, white wine vin., garlic, green onion, tarragon, sugar, s&p
Or one where you shred lots of things like cabbage, carrots, lettuce and let your guests mix them with olives, lemons and pickled peppers...
There are also several Scandinavian things involving potatoes and smoked salmon and sour cream.