The main two methods I have been using are:
Darkslide: I liked this method because it wasn't cumbersome but it didn't offer complete protection from light.
Box: Shooting into a box worked really well, but it was a hassle having a box around at all times when you were shooting, and it felt awkward attached to my SX-70.
SO here is what I use now and it works pretty well and is also easy to carry around!
It's basically 2 pieces of black paper taped together with the top open. It attaches on the front of my SX-70 with a small clip and 2 slits are cut on the back so it can fit over the bottom of the camera better, allowing the film to eject properly into the sleeve.
Also a unique feature about this sleeve is that there is a cut-out on the bottom that will allow you to slide out the film into the sleeve. One of the big reasons why the previous methods of shielding film for me didn't work was because the film doesnt eject out all the way! Which made it very awkward to slide the film out of the camera and into the darkslide/box etc. Now after my film ejects, it is evenly protected from light :D and I can remove the sleeve and fold up my SX-70 and be on my way!
The sleeve also allows you to quickly move the film into a different temperature environment quicker too. If you want to heat up your film under your armpit or on top of a furnace... etc.
Enjoy my instructions on how to make this simple but effective Light Shield for your SX-70
UPDATE: Video Tutorial