I've talked to a lot of people recently with jobs that involve staying away from home for long periods - away from climbing and climbing walls. Maintaining or even increasing their climbing related strength can seem impossible. But some job placements do provide access to weights gyms and we can use these to work hard on basic strength at least. With free weights we are looking to replicate the climbing movements. Lat-pulls downs/weighted pull-ups are priority number one. You can do a lot of them without getting too tired. You can simulate undercutting with seated rows, either pulling through the ROM or doing static locks with a really heavy weight. Beyond these essentials, you can simply simulate the movements you are weak on, and work on them. The second priority is working on core body strength. There are thousands of exercises and bits of kit out there. Personally I like to keep it simple and use Clean&jerk and front levers on a bar. Don't forget to do a little work on the antagonists for each muscle group you target!
So what about fingers? Well gyms are a little frustrating from a finger strength point of view. In the past, folk used slings hung from a bar to do one and two finger pull-ups (on two arms they aren't as a hard as they sound). Metolius have also invented the handy bits of kit in the pic above. I would never think of using these at home. But if ever get a job offshore, they would be the first thing in my bag!