I've got (sadly down in Poland, not with me):
- German bayonet Mk 1871 (a variant not for combat purposes, but parades only)
- another szwabski bayonet (don't remember the type, but I guess it's parade version too)
- Polish eagle (I think it's an officer one, pre-1939)
- Russian helmet (II WW, post war use in a fire brigade)
- some empty shells, probably I, II WW (cal 8 mm, they might have been from hunting weapons, for the house was a forester's domicile, found on my own yard)
- I also found a 7,62 mm (? - it was deformed, probably from a Soviet MG) round inside a piece of firewood :)
My dad had much better 'luck'. He told me, that when he was a boy, he and his pals found a German MG, but discarded of it. They even had real pistols as toys. Also when he was a forestry school student, they had some practise in woods and sometimes the whole group returned with German helmets on their heads !
Edit: I know you were asking about Polish weapons, but I couldn't help :) Besides, some might have been used by Polish army (or during Silesian uprisings).