sorry to hear about your situation. It is for sure a very difficult situation. The fact you are feeling anxiety is natural and very understandable, so don't be down on yourself for that. The fact you have survived shows your strength.
I think you are seeing the situation with great clarity.
Living with ongoing anxiety is definitely best avoided if at all possible. But you don't want to make a bad situation worse! Again, do not make a bad situation worse. Therefore you need to be very careful about what you do. This is not a time to act rashly - but a time for strategic thinking and planning that may take some time to put into action.
First thing as already stated: make absolutely sure they cannot track your online activity so they can't find this question. TOTALLY CRITICAL !!!! One option is to install a different browser to whatever you usually use and only read this topic on that browser and make sure there is no shortcut to the browser on your desktop or Start Menu etc. You can open it by typing the name into the little search box on the Windows menu assuming you are using Windows 7 or so. And make sure the browsing history is also deleted after you use it. So if you use Firefox then also install Google Chrome and hide any reference to it. Alternatively you could just download CCleaner and run it after using your PC to remove browsing history. How much you need to do depends how PC literate they are.
As I see it, in regards to leaving the major problem is money - in the short term and longer term. You need cash or goods of value to leave and set-up elsewhere and then you need some form of employment to sustain it. You may not have this covered now but you may be able to work towards it over time. (ie. selling things on ebay or at a market and adding to your skills by learning online - eg. learning to touch type, learning marketing, etc....).
If you are employable and jobs are available in a nearby city then that would go a long way towards a successful outcome for you. I don't where you stand on this ??
Is it necessary to leave the country ? Couldn't you just move to another, distant city ? Would you need to change your name ?
The secondary problem as I see it is the papers. First, as suggested by someone else, I would research the situation with regards to obtaining new papers. That's the best option. There must be some procedure for issuing new papers (when they are lost etc). If you can get a post box at a post office and get new papers sent there. If none of this is possible then you are back to trying to obtain the originals.
The locked door - many door locks can be picked. You can make a lock pick or a thing called a "bump key" (see google). If you are lucky and it is a common lock you may be able to get one from somewhere to practice on first. I would actually advise this because it is possible to damage the lock (without opening it) which could make them suspicious. So be careful on that.
Alternatively, depending on the lock, it can be possible to wedge a bit of paper or cardboard into the part where the lock bolt fits into - to stop the bolt from locking in securely. This can work. If done properly if will seem like the door secures properly but it can then be opened if tested. Again, this would require some practice to ensure it doesn't fail - but it may be possible. You could read about it online.
The locked bag - Can you take the whole bag with you ? If not, is it padlocked ? Bolt-cutters from the hardware store will cut-through most padlocks - but again practice first. They may require a bit of strength depending on the padlock size. Alternatively, can you just slash the bag open with a knife or similar, take your papers and leave the rest ?
If none of that seems possible now then you are down to "harm minimization" tactics. You are probably doing all this already but anyway..... - Stay away from him and home as much as possible; try to spend as much time at work or at a friend's house as possible; try to identify what things will set him off and avoid doing them; try to do things you enjoy to take your mind away from it, like reading drawing, etc.
It is important to be very clear in your mind that these are his issues and nothing to do with you as a person.
Also try not to view the situation as "a prison" even if it feels like one. Making it "a prison" builds the psychological impression (in your mind) that it can't be escaped. It is not a prison but rather a very difficult and bad situation that you have survived, but ideally you need to leave.
My left field suggestion would be to try to do nice things for him on the basis that it's harder to be mean to someone if they are being nice to you and doing nice things for you.... It may create some psychological conflict in his mind/emotions if he goes to be mean to you but knows you have been kind to him. This may be hard to do and it may not work but I can't seen any risks in trying it.
I hope something in there helps.
Be strategic. Be careful.