Kerosene,
concerning Poland and landing on international airport - I am surprised they still have it in AIP (do they?),
I am based in smaller Warsaw airport (EPBC, with Avgass, lots of GA trafick), which is not international, and I never use Polish international airport going abroad to/from Schengen,
I do not think you may have any problem landing in any Polish airstrip if comming form Schengen - thou would be good to call apt beforehand to make sure they are open and check for Avgass (there is a good
Portal | dlapilota.pl with all airstrips)
regards,
Greg