'She's the sort of person who buys her own drinks' - a withering put-down of someone who doesn't stand their round, because, basically, they think they'll be better off if they don't; they're not planning to stay long, or they're only drinking halves, so why should they buy drinks for eveyone else when they won't get the equivalent back in return? The reason they should, of course, is that it's what you do; it's central to English (British?) pub culture. It's an acknowledgement that, in this context, you are not just a self-interested individual but part of a larger community, even if that community is just you and a couple of mates. It recognises that this isn't a one-off occasion, but part of a continuum, in which unequal contributions can be evened out over time; again, part of something bigger than the individual and the moment. It's a homage to tradition; a rite by which we identify ourselves with a particular heritage. Buying your own drinks is a certain kind of meanness which passes itself off as the opposite but's more than that; it's a stand-offishness, a refusal to fully become part of the group.
So... there's a toilet here at the yard. Not a bad one, in fact, as these things go. Not as clean as it might be, of course, but spacious and most importantly, warm. Now, when there's a toilet on the bank, a boat dweller will use it at every opportunity, to avoid too frequent filling and consequent emptying of the on board facilities. As toilets around the system vary in the level of cleanliness and facilities they offer, I always carry with me a 'toilet bag' containing among other vital accoutrements, a toilet roll and a pack of Parazone (or equivalent) wipes. Paranoid I may be, but itnmakes me happy.
The loo here is used by the people working here and other moorers, when there are any. Sometimes there's a loo roll there and sometimes there isn't. When there is, it's impossible to know who's provided it. Because sometimes there isn't one, I always take my bag with me (well, it might need a clean anyway). So, when there is a roll there, should I use that one, or my own? If I use the one that's there, then I am honour bound at some stage to provide a replacement. But if I always use my own, then I don't have to worry about it. As I thought this through, I realised that there is a real parallel with the pub scenario. I could just look out for myself, and not owe anyone anything. Or I could be part of the wider community, using, and providing, the communal resources, without worrying too much about whether it's my turn, or if I'm providing more sheets than the next person. And I realised the answer it clear - next time I must leave the roll behind when I leave.