I have a couple of plastic trash cans that don’t have knobs, but they do have a little handle thing on either side. You loop the handles of your plastic shopping bag on each one and they hold up well. I have had these several years and I believe they may have come from Wal-mart or K-mart.
For larger trash bags (Hefty bags, etc.), there are patterns that have a rectangle box made of wood, with a lid that is square. You fold the top of the kitchen-sized Hefty bag over the top of the box and then set the lid on it to hold it on the box. The lid has a door that swings up, so you can deposit garbage in it without taking off the part that holds the bag. When the bag is full, then you can remove the whole thing and take the bag to the curb or dumpster. I bought mine from a crafts market but I know there is a woodworking pattern for this thing floating around somewhere. I can’t use it in my present tiny apartment but I’ve used this thing in my houses and there is never a problem with insects or odor if you take the trash out once or twice a week.