1. Defend against format obsolescence. Prefer plain-text formats, or at least ones that can be mostly-understood by humans, like markdown or semantic XML. (And not, say, PDFs.) For audio-visual stuff, prefer the simplest kinds of highly standardized and common formats.

2. If you need a website, prefer a static site generator. If you need a dynamic site, periodically export a static version.

3. Don't count entirely on the hosting service, store offline copies (as a standard zip file) alongside other content of interest to heirs, such as a will. Distribute redundant copies to relatives.