My brother wrote this very informative and hilarious book of backpacking tips and stories and has briefly dropped the price.
Sorry if this should be in forums - but the info is genuinely extremely good value for $1, not just for backpackers but general travellers. Also, it has some very amusing stories.
He's spent 1100+ nights in hostels across 40+ countries and has done plenty wrong - getting lost in the Sahara desert, having a sword held to his throat, AK-47’s pointed at him, pooping himself in public, etc.
Disclaimer - there's some rude language in it.