If you dont want the technical way, you can go into cheat mode in NEI, Fill your inventory up with your crap, save it, empty your inventory, fill it again with other items, and save it to load 2, rinse and repeat till 10, then you can go into your new world and dump all yo shiz into chests, then go into your old world and repeat. Much more easier to understand if you have never modded or messed with any of that stuff.