Also, directives typically describe goals, not the way to reach them. That gives individual countries some freedom.
For example, Directive 2015/720 requires member states to reduce single-use plastic bag use by 50% by 2017 and 80% by 2019, but doesn’t tell anything about how to do that.
Denmark taxes companies giving away bags, Ireland taxes every bag sold, the Netherlands made it illegal to give out free bags (with exceptions), Serbia (not EU, but aspiring to become an EU country) taxes manufacturers and importers of plastic bags, etc (https://en.m.wikipedia.org/wiki/Phase-out_of_lightweight_pla...)
And yes, there likely are opportunities to game this. If you buy a can of beer or a single-use bottle of soda in Germany, for example, you pay a deposit that you get back when you return the empty vessel. Often, you can buy the same vessel in Belgium, where the deposit is lower, or the Netherlands, where deposits only exist for bottles of half a liter or more.