Tabs Outliner features tab/window unloading, crash backups and the ability to backup all active/unloaded/crashed tabs/windows.
https://chrome.google.com/webstore/detail/tabs-outliner/eggkanocgddhmamlbiijnphhppkpkmkl?hl=en
Session Buddy allows manual session saving, exporting and restoration.
https://chrome.google.com/webstore/detail/session-buddy/edacconmaakjimmfgnblocblbcdcpbko?hl=en
OneTab allows "bookmarking" of all open tabs onto the extension's local page. It automatically deletes dupes, separates saved pages into rename-able categories that state the number of pages saved each time, and allows moving/rearranging saved pages (but unfortunately not categories).
https://chrome.google.com/webstore/detail/onetab/chphlpgkkbolifaimnlloiipkdnihall?hl=en
Those might not be built in functions like some people want, but they work well enough to compensate for Opera's shortcomings.
I actually use a combination of all three for session management, tab unloading/recovery and bookmarking (with dupe management) instead of the browser's built in functions because they all provide invaluable features that Opera itself lacks.
What's more, the extensions can be temporarily turned off as-needed to avoid crippling "load lag".
Anyway, as great as it'd be to have all those functions (including crash recovery) built into Opera, I can't help but worry that the potential bloat could slow down the browser if the devs didn't allow the session manager component to be disabled until/unless it's needed. The same goes for the bookmark manager, which remains an "always on" feature.
But given that they still haven't even coded an exit confirmation prompt to stop multiple tab closure, or a universally supported import/export function into the bookmarks manager, it's probably safe to say they wouldn't "think of everything" in regards to crash recovery and session management, and that their inclusion of such features could actually turn out to be worthless (or even a nuisance) if implemented thoughtlessly without regard to the "power user" experience.
