The basic things needed to tie dye are white cotton t-shirts, soda ash, rubber bands, procion dye, plastic gloves, a way to apply the dye (squirt bottles or eye dropper and small containers), a place to apply the dye (a plastic container or on top of a plastic bag), synthropol laundry soap (or similar) and a creative mind.
A more advance setup includes a plastic table for a workspace. A shelf to dry dipped t-shirts and to store dyed t-shirts. Multiple plastic containers with wire racks inside to rest t-shirts on while they are dyed. And of course a washer and dryer machine.
Tie Dye supplies can be purchased online at Dharma Trading Company in San Francisco, California.