latte and a packet of crisps

Living on a boat and maintaing a house money is tight. Where in the "good old days" I was able to go out to lunch and buy a packet of crisps, or nip into Pret for a skinny (of course) Latte.. now I think about every penny (71p) that I have in my purse. For lunch I am living off home made sandwiches and re-filling up the same bottle of water that I have had for over a week .. (I wonder if this is hygienic?).. How I long for the days of wondering around boots buying a months supply of rescue remedy.. now I have to make the bottle last and only use it in emergencies.. perhaps this is why I am so stressed???