I know of Poles getting cheap flights to Doncaster or Liverpool to go to Primark etc for clothes
To be fair, Primark is ridiculously cheap compared to most European shops!
food can often be cheaper elsewhere too.
All depends what, I think. Certainly decent Asian food is far cheaper in Berlin than in Poland, but raw ingredients are cheap in Poland. There's a reason why meat is sold per kg in Poland and per 100g in Germany.