The hostel owner in Lisbon charged me 2 euros for a towel, then showed me the free ones behind the desk
Turns out most hostels have loaner towels and adapters if you just ask at check in instead of renting them. What's the dumbest thing you've paid extra for at a hostel that was actually free?
Paid 5 euros for a padlock at a hostel in Berlin when I already had one buried in my bag. Felt like a total idiot digging it out ten minutes later. Now I just dump everything on the bed first thing and check before I buy anything.