Be careful with this. I've seen too many people burned by business owners who do that, especially when you're not on the books. The owner of the body shop I worked at tried that shit, he
was a long time family friend and I thought I was just helping him out. I was going a week and a half to 2 weeks between pay and he owed me a couple weeks on a revolving IOU. Always talking about how the business isn't doing well, customers owe him money, blah, blah, blah. Then one day he pulls in the shop with a brand new $130,000 RV he was bragging about paying cash for.
I made him pay me everything he owed me and made sure I got paid, cash in hand, every week after that. There were a couple times I had to take shop equipment as collateral, but after I hawked some of his tools the last time he tried it, it stopped.
I've had a few friends lose weeks of pay when they were let go and never got back pay. Under the table? "Fuck off, prove it" Those were mostly lawn care places, they're known for that.
What you're doing is giving their business a interest free short term loan. Payroll is part of running a business, if they can't do that I'd question the future of the company. Plus, I bet they don't sell jerky on credit.