Dunno if this was mentioned but
when you are taveling into Poland (or generally in the EU) you are required to have a "green card" which is basic insurance. Make sure you get this, or you would have to purchase this (and Im guessing every boarder crossing) but once you get it from the rent-a-car, it should cover all of EU
Geico does have Europe auto insurance (country by country though) Amex plat also has insurance (which with extra fee can be primary ) and alcohol limits is very strict. 0.02 on Poland, so be careful. Make sure you got a international drivers license (from AAA)