I'm not sure which is more unrealistic, getting people not to litter or getting countries to use photo/bio-degradable plastics (especially plastic bags). The perfect example would be Cambodia. In truth I have never seen a place with more litter (outside of a dump) but upon closer inspection you will see that most of it is plastic bags. Khmer are *really* good about recycling stuff they can actually get money for (testimony to the dire poverty), I tested this multiple times by placing plastic and glass bottles out in plain view only to have them swiped in less than 20 minutes, where as plastic bags would never move. In the rivers, streets, yards I would see plastic bags everywhere. The best thing would of course be not to have them, use paper or cloth but that is probably the most unrealistic.
In the US many grocery stores (especially the larger chains) use photo (will breakdown in light) or bio (microorganisms can break it down) degradable plastics; I think this is still a really poor idea in countries of comparable wealth but changing developed countries can sometimes be harder than changing the developing countries.