Essentials to live in Poland

Years ago, this was an issue; no longer. Most items are available in a range of shops, and more often than not at advantageous prices. I suppose that if there is a particular product or brand that you use , it's better to bring it from home. (In my case, it's Tylenol-style headache pills; the equivalent is not available in Poland or some other European countries. As that's about all that occurs to me, you can see that one doesn't want for much here.)

I fly back and forward to the UK once a month and always pack a few packs of bacon and kids clothes are about half the price. PlayStation games much cheaper but Amazon deliver them to Poland

Electronics from the US, also some american brands from cosmetics. Imported items are usually broadly available in Poland but slightly more expensive.
Berocca (multivitamin tablets) from the UK.

Basically a little items that brands of you don't want to change. The equivalents are available ( I had to smile about the bacon as Poland is a pork country much more then the UK) but it can take you time to find one that exactly matches your taste.