No Money

Yesterday morning I stopped by the grocery store and had my rickshaw driver wait for me b/c I was planning to be quick. I got my little basket full of stuff and went up to pay. About the time he finished ringing me up I had finished emptying my purse onto the counter and my wallet wasn't there. I knew I'd left it at home so I wasn't worried that I'd lost it, but I don't actually know the word for 'to forget'...I know 'to remember' but that one wasn't coming quick enough and so all I could do was look at the guy and say 'I don't have money'. I think he probably saw that one coming and all he said was 'No problem. Just remember next time' and he gave me my receipt. I had only gotten about $15 worth of stuff but still, I only go to that store about once every 3 weeks so it's not like they know me all that well. I went back and paid my 'bill' about 2 hours later and they were surprised that I came back. How do they make any money if they just give things away?!?