J.S.
I used to tie dye all the time. My girls had wonderful, colorful onsies, shirts, and dresses!
If you are just going to dye a few items a kit is your best bet. It will have everything you need. You want to get something that has procion dye. It is specifically made for this type of dying and will give you nice, bright, longlasting results. The soda ash softens the fibers so they take the dye better.
Here is a link to a good kit, so you can see what I am talking about. :)
http://www.amazon.com/Jacquard-JAC9320-Tie-Dye-Kit/dp/B##...
My local Beverly's sells this same kit, so you may be able to find it somewhere near you as well.
The key to good, bright tie dye is technique. Using a product like Rit requires dying the whole item with the lightest color, then removing/moving the rubber bands around then over dying the item with the next darker color, and so on. This creates a kind of muddy, subdued result and takes way to long.
With Procion dyes you fold and band the item in the pattern you like then squirt the dye directly onto the item in the areas you want a certain color. You can put all the colors on at once. For instance, for a spiral pattern you lay your shirt out flat. Then pinch (finger and thumb) the place you want to be the center of your spiral and start twisting, keeping the shirt flat to the table, until the whole shirt is twirlled up like a snail shell, or cinnamon roll. Then put a rubber band across the center of the resulting circle, then another band, then another until. This will leave you with a 6 slice 'pie'. ( I hope you can picture this!). Then squirt a different color dye directly onto each pie slice. You can use just two colors and alternate sllices. Don't worry if they 'bleed' from one slice to the other. That is supposed to happen. Once you've done one side, turn over your shirt and do the other side of the pie, squirting the same colors on the same slices. Put the shirt into a plastic bag and leave it over night. The next day, remove the bands and rinse it out with cold water until the water runs pretty clear. Don't worry about sqeezing and wringing it, the colors will not run together at this point. Once the water runs fairly clear, pop it into your washing machine on hot water with just a little detergent and wash and dry as normal. This sets the dye and it shouldn't fade after that. If you do several items you can wash them all together. They will not fade on one another even if you have one shirt that is yellow and pink, and another that is purple and black! This amazed me the first time I did it. :)
Have fun. It can be a bit addicting!
Oh, I almost forgot. Use 100% cotton clothes to dye. Men's packaged t-shirts are great! Polyester does not take dye so the colors come out faded on blend fabrics.