What is the best way to keep drinks stable on the couch?

An armrest caddy with a deep cup well that drapes over the armrest is the most stable option. It does not slide when the cushion shifts and it does not require a side table.

Should I cover the couch for Thanksgiving?

Generally no. A couch cover slides under guests and makes the whole thing feel temporary. Spot-treat the next day instead.

What about pets at Thanksgiving on the couch?

Pets get the floor or another room during the meal. The couch is people-only for two hours.

When the couch is the dining room: Thanksgiving overflow

The geometry problem

Most American apartments built after 1990 have a dining area that seats four. Thanksgiving is for six to ten. The math does not work. The couch becomes the second table.

This is treated as a failure of hosting. It is not. It is the most honest acknowledgment of how people actually eat together. The work is making the couch behave like a dining table for two hours.

Five small fixes

Use real plates, not paper. Real plates do not blow off the couch when someone gets up.
Use low-sided bowls for sides. Stuffing in a flat plate ends up in a cushion. Stuffing in a low bowl does not.
Give every couch seat a small tray. A wooden cutting board works. So does a silicone tray. So does a hardcover book turned over.
Put the drink station off the floor. The floor is a stepping accident waiting to happen.
Skip the soup course. Trust me on this one.

The drink station, specifically

Drinks at couch-height Thanksgiving are the most common disaster. Wine glasses on a cushion is the worst possible setup. Beer cans on the floor is the second worst.

An armrest-mounted caddy or a low side table next to the couch is the right answer. The drink needs to be in the same field of vision as the food, or it will be forgotten and kicked. We have spent a lot of time on this problem. It has not been solved by any single product yet, but several products help.

What to skip

A formal seating chart. It will not survive the first plate.
Glassware that is too thin to survive the couch.
Tablecloths on the couch. Just clean the couch the next day.
Centerpieces. There is no center.

Why this works

Treating the couch as a legitimate second dining area is more honest than pretending the dining room is bigger than it is. Guests relax. The host stops apologizing. The meal moves between the table and the couch the way it should.

Thanksgiving in a small apartment is not a constraint. It is the most New York version of the holiday, and there is no shame in it. Plan for the couch. The couch will rise to the occasion.