I've 'slept rough' at Manchester Piccadilly many, many years ago, it was quite surreal as the concourse was just littered with hundreds of people asleep! (Felt like being in a real life Resident Evil game to be honest!)
Once 'abused' the East Midlands Railway red dot scheme too, spent the day travelling on their trains and then ensured the last one I caught dropped me off in Nottingham as that was the origin station for the scheme the following day...luckily there was a 24 hour McDonalds close by to Nottingham station which happily allowed me to sit in drinking coffee for a few hours
Too old to endure such feats these days and always plan in hotels if required!