Although this list is sort of sparse; here are some handy posts I've come across on Reddit:
What's your pic or it didn't happen pic? – maybe not necessarily helpful but def entertaining.
Favorite thing in your 'saved' section? – again not inherently helpful but there are some helpful threads in there.
And here's Reddit's 'Museum of Filth – Although not an Askreddit post, it's very useful to understand some of reddit's ongoing jokes like 'something something 2 broken arms'. Obviously NSFW and NSFL – some of the stuff will make your soul pucker.