ThrainSil,
Any single item can not have mulitple resistances, ie... 1 type of resistance (bludgenoning, cold, acid, ect...). You can have mulitple items with different types of resistances but lets say you have a cloak of cold resitance 5/- and a belt of artic resitance of cold 10/- .... You would NOT get a 15/- to your cold resistance you would get the greater of the the two resitances, in this case 10/-. Now as far as taking a feat and getting a bonus, I am not sure how that works but it would make since to me that any "natural" resistances would be cumulative to item resistances. (speculation here) But 5/- natural cold resistance would stack with a 5/- belt of frost giants for a total of 10/-. Need a GM to confirm or deny this but I hope this rambling helped.