Используйте это:
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
plistpath = [[NSString alloc] initWithString:[documentsDirectory stringByAppendingPathComponent:@"Product.plist"]];
А потом
[array writeToFile:path atomically:YES];
[Whatever [Array or Dictionary] you want to Write in Plist]
И для получения данных из Plist
NSmutableArray *Yourarray = [[NSMutableArray alloc] initWithContentsOfFile:plistpath];