Routines are important because those with GAD do not handle new situations well. Routines allow them to control their anxiety in that moment and feel a sense of calmness. Comfort zones pretty much work the same way except that they need one major comfort zone and one minor comfort zone. What do I mean by this?
For most sufferers, home is their major comfort zone. They can handle their anxiety with family in a nurturing way. They aren't in public and can have an attack without judgement. It can even just be one room where they feel the most comfortable. For Twin, this would be the bedroom. It shields her from anything that could bring on an unexpected anxiety attack. She calls it her "bubble", which isn't uncommon for anxiety sufferers. Most of them will refer to their major comfort zone as their "bubble".
For a minor comfort zone, this is where they feel a little anxiety, but know an anxiety attack will most likely not happen. A minor comfort zone can be a car, a friend's house, or even the lake. It all depends on where the person has fun. It keeps their mind off their anxiety (and anything that could be currently causing the anxiety like a situation at home). Since Twin and I love going to our local park, that would be her minor comfort zone. We are able to enjoy nature, staring at the Brazos River, and just talk. But we also enjoy sitting out into the back breezeway at night (since she also has Social Anxiety), pouring our hearts out.
So remember, comfort zones are important for those with anxiety. They need it to cope with anxiety. Be there for them and allow them to stay in their comfort zone. They'll appreciate it more than you know.