That's an excellent and very practical question! For most standard urban or commercial trash cans—the kind you see in parks, offices, or on sidewalks—the liners are typically a standard size. You usually do not have to buy special, proprietary bags from the original manufacturer. These cans are often designed to work with common, commercially available plastic liners like 33-gallon or 55-gallon trash bags, which you can find at any hardware or janitorial supply store.
However, the key word is "most." It's always crucial to check the exact dimensions of your specific bin. Some designer or specialty urban cans might have unique shapes or sizes that require custom liners. The best practice is to measure the interior dimensions of your can (height, width, and depth) and compare them to the bag specifications before buying in bulk.
Using standard bags is almost always more convenient and cost-effective. So, in short: you can likely use off-the-shelf bags, but always double-check the fit to avoid tears and spills. For a perfect match, measure first!