You'll need a stripping guide, I suggest a #8 one. To figuyre number of guides you need figure 1 guide per foot of rod length, this includes the stipping guide. So for a 6'6" fod, you would need 1 stripping guide and 6 snake guides, plus a rod tip (or top) guide. Also, don't forget to get a rod top and size A thread in the color you desire. A thread burnisher is worth having (they are less than $2.00 usually) to pack the thread after the guide is wrapped (I don't remember if Cabella's includes this in the rod building set), and don't forget the rod finish.
A rod case of some sort with a cheap and very strong one being PVC sewer pipe in 1 1/2" cut to length with a PVC cap vlued to one end and left unglued so it provides a friction fit on the other side. And don't forget a rod bag to protect the rod from scatches when it is in the rod case.
The spine finder is really not necessary to build a rod or find the spine. To find the spine either: 1) place the butt portion of the rod section on a table while holding the tip of the section with your index finger; then use your other hand to bend the section by using it to put pressure on the middle of the rod section; roll the rod section while putting pressure on it and the spine will automatically roll up to the top. (the blank will sort of "jump" or "kick" when the spine rolls up; or 2) place the thick end of the rod section under the edge of a table; hold the section with you fingers at the top of the section; put upward pressure on the section with you other hand and the spine will roll to the bottom.
Why spend the money for a spine finder when you don't need to? Instead, use the money to get something else (like the best quality TiCH snake guides).
Enjoy the rod building process, take your time, and let us know how it turned out. It is addicting though, just like tying and fishing.