Recycling your zip-top bags? Pish! Re-using your dental floss? That's nothing! Here's some REALLY cheap ideas.
1. A few years after my divorce, when I didn't have much money, I dated a man who held radically opposite political views from mine. He was racist, sexist, bigoted, and you name it. However, every Wednesday, he stopped at a pizza place and bought 2 large veggie pizzas, which he then brought over to my apartment. He and my daughter and I would have pizza for dinner. We kept the leftovers, and my daughter and I had pizza for dinner at least one other night that week. Yes, I dated him for food.
2. About 10 years ago, my new husband and I lived in a home built back in the 40's, with an unfinished basement with one of those 2-sink washtubs in it. The washer emptied into one of those tubs. Previous owners had installed central air conditioning as well as a humidifying system, and both of those drained excess water into the other side of the washtub. I started saving that water in a gallon bucket and then pouring it into the top-loading washer. I figured it was relatively clean water, since it was either excess humidity removed by the AC, or "leftover" water from the winter humidifier. It certainly wasn't drinkable, but with some detergent and added hot water, it was perfectly fine for washing clothes. I think this is called "gray" water.
A washing machine fills up with water on the basis of "is it full?" unlike the dishwasher, which fills for a specific time period. Different types of clothes absorb more or less water, so the washing machine has to get filled to a certain level. This meant that, no matter how much gray water I poured into the washer, if it was set for a full load, hot or warm water would fill the washer the rest of the way, and not overfill it. On a good day, I could fill the washer halfway with gray water. It was "our" water, why waste it?
And, of course, I hung a lot of the clothes on lines strung in the basement....