The topic most talked/asked about on Facebook is, by far, about warp separators.
Basically, you want to use something stiff that won't also become compacted by the tension of subsequent warp threads above it.
The reason you want a warp separator is to keep the threads from slipping between each other. When that happens, the warp doesn't go around the warp beam at the same diameter and that leaves you with tension issues that will make weaving a nightmare. Warp separator prevents that.
Laura Fry has an excellent post about her experiences, over the years, regarding this topic. Ever since I learned about this, I have been using match stick blinds and they are, in my opinion, the best ever things to use. I realize that not everyone may like them and we all have our favorites, but I've tried all manner of materials and the match stick blinds win, hands down.
If you're the handy type, lath comes in bundles of 50 at the hardware store. You can cut them down and sand them and they make wonderful warping sticks.
Now, on to Laura's post. Enjoy!