I'm glad you have an appointment scheduled for after Christmas with your therapist - I always find it is reassuring to have that planned so that you know you will have someone to talk through everything with and try to decompress. Maybe even plan something nice for yourself to look forward to for when you get back from Christmas? It is tricky with no service, I'm sorry, it definitely does make it feel more isolating, I get that. If you do manage to get any service/wifi, there is also these forums that you can check in with, even if it is just to offload what is happening and going through your mind to externalise it.
It can be tricky to leave and go outside, especially when people start questioning you, and there is only so many times you can say "going to the toilet"... But maybe having some things prepared to say like "I'm just going outside for a walk to get some fresh air/sunshine", "I'm feeling a bit stuffed, I'm just going to go for a stroll", "I've got a bit of a headache, I just need to go outside for a bit". Sorry that sounds weird typed out but hopefully you get what I mean.
Everyone's different but I have a list of things on my phone which I personally find can help to look to when I'm low or anxious or overwhelmed... including listening to music, going for a long walk outside, journaling (doesn't have to be pen and paper, just something to try to organise your thoughts a bit into words and get them out of your system), wash/submerge face with/in cold water, organise cupboards, clean/vacuum (I know this is an odd one), slow breathing down to 8-12 breaths per minute and try to focus on breathing, grounding techniques (sensory, breathing, physical). Sometimes these don't work well, sometimes they do help a bit. There is also the Smiling Mind app (I think there are some parts that you can access with no service/wifi) which you may also find helpful to ground you.
It is difficult though, I'm sorry if this is a bit of a ramble. But hopefully you can find some things that help you to get through this period. Again, please feel free to chat more if/when you feel like it. You're not alone.