The bag that comes in the illford box + three tiered box (normal film box), tape it and mark it exposed film + process (E-6 / C-41). They can read the edge codes, but...
If you have that black plastic sheeting from the hardware store (comes in rolls), you can tape your own bags together. Just be sure your "design" is sound.
Also, for quick fixes I've put sheets in ziplocks and then carefully wrapped that in foil, but I wouldn't trust that to send it to a lab, just for around the home.