With offline material! If you can afford to take with you some hundreds GB of data and a laptop you're set. For example, let's say you want to learn Erlang: ins

With offline material! If you can afford to take with you some hundreds GB of data and a laptop you're set. For example, let's say you want to learn Erlang: install the VM, keep an offline cache for dependencies (with their respective docs), Erlang docs and mirror devdocs.io. If the skill in question is not tech-related you can carry a lot less data probably too (find some manuals).