fishdudein
Fishaholic
Whatever it takes to get the beneficial bacteria "started" in your new tank. Did the driftwood come from your old tanks? If so, you have already imported a good source of bacteria into your tank. The sponges would be another good idea. If you don't want to mix two different colors of gravel (what I interpreted you as meaning), then the gravel in a sock should work- I have even put some of my old gravel into a ceramic or crockware bowl and set that in my aquarium. Plants, decorations, anything from your old tank with a surface area that bacteria can grow on will help but the filter media and sponges with their large porous surface area are the best sources.
good luck! hope it all works out