Local restaurants. I stopped in a cafe near my studio and asked the owner if he would mind saving the mayo, relish, black pepper, cinnamon etc containers for me. He was more than happy to, because then he didn't have to throw them away or haul them to recycling. It was a win-win situation. And 3 years later I'm still using the free containers that it took him just 2 weeks to collect! So, if you're in need of storage containers, give it a try! Ask nearby restaurants to help out a local artist!