how do you track expenses you pay cash for?

[Morgan Gruelle]

I am wondering how I can account for cash expenses. I have a rental property that I did not have time to paint so I paid a friend cash to paint the rooms over the coarse of a few days. I am wondering how can I track this expense for labor since I do not have an invoice for the work or a receipt from paying him. Should I just get one of those cash receipt notebooks and let him write me up a receipt for the work? Would that be sufficient at tax time in case of an audit? Additionally I had to replace a couple of broken appliances, which I purchased off craigslist also for cash. What is the best way to account for these expenses for tax purposes?