Resources importer is one option, as is the new site initializer. Custom code invoking the Liferay APIs to feed the data, or even one or more Groovy scripts to do the same.

There's no tool, that I'm aware of, which will do this for you. Each of these options would be some amount of at least transforms but more likely some development aspects, but they are each doable.

For files, you have two options:
1) Webdav: You can connect to the document library using webdav (map network drive) and just copy the files and folders to the server

- No metadata (original author, timestamps,  ...)
- No permissions
- If you want to link to them later on (e.g. images on a website), it can be difficult to find the ids

But if you just want to add the files, have just a few folders with permissions (where you update them later manually) it isn't a quick way to do it.

2) Through the API.
e.g. using DLAppLocalService
https://docs.liferay.com/dxp/portal/7.2-latest/javadocs/portal-kernel/index.html?com/liferay/document/library/kernel/service/DLAppLocalService.html
With that you have far more control, but it is a lot more work.

For content:
Content is more work. If you just want to add webcontent, I would create an importer that processes all my content and calls use JournalArticleLocalService to add a new webcontent for each of my exported html items.
If you want to add pages to, that's more difficult. You need to create the pages, put portlets on them and then configure them. e.g. configure webcontent portlet to show the webcontent you create with JournalArticleLocalService.