Although that tiny pullout tray only holds one drink, in my experience, the armrest contains sufficient space to hold two drinks and the warmed mixed nuts on AA. So I've never had any trouble sharing armrest space with my seatmate, as the armrest contains sufficient space for both drinks.

Of course, on AA, the pullout tray only appears on 757s and A300s, since the F seats on the other mainline planes each have a personal swing-out drink tray (instead of the shared pullout tray).

On other airlines, the armrest may contain too little space for two drinks.