You can do a boxing circuit at home, but you'll miss out on sparring. Speed work, heavy bag conditioning, slipping, shadowboxing, roadwork, skipping and so on. You'll miss out on sparring. The most important part. Same deal with kung fu forms, karate katas or whatever. Not even sure how you would go about training wrestling or bjj at home.
That said, you can still go to a gym or dojo a few times a week, then do the same shit, or ancillary training at home. You probably should be doing that if you want to progress. Even if it's only 15-20 minutes of practice a day. I'd suggest going to a gym, even if you have to take the train or a bus, making a day of it and letting the coach/instructor know what your circumstances are. Even if you're only getting experienced eyes on you once a week or once a month, it's better than nothing. They might even be able to put you in touch with more local people that you're unaware of. It might just be back yard training instead of a proper gym, but it's better than nothing.