" know not what blade steel is best for World War III, but for World War IV Obsidian is highly recommended "

well, if you're going to challenge me to get semi-serious about this topic.

what creatures are likely to be surviving after WWIII? On land, I'd say its probably rats and crows. The scavengers and the carrion feeders. Rats are great survivors and will eat almost anything. Crows are pretty smart.

These would be the creatures that you would have to live on. And you probably would do just fine with a good slingshot, a crossbow, or an airgun.

It seems to me that an airgun with moderate power (doesn't require high power) would be more than adequate. And it's a very sensible choice - it could be re-pumped and fired for a long, long time.