First, don't worry too much about maybe having forgotten something with your tail kit order. There's not really anything that can't be installed later when an epiphany occurs and you realize that you need some sort of this or that.
Now, just food for thought, some things to consider:
- VOR antenna placement (if using a Cat Whisker). If up high in the VS, might want to go ahead and buy some conduit, if down low under the HS might want to buy some extra .025 or .032 sheet to make a doubler out of. Why you're at it, you might want to go ahead and pick up a good length of 3/4" x 3/4" angle which can be used to fab a lot of things.
- Extra nutplates and screws if you decide to mount fairings with screws vs. blind rivets
- Fiberglass supplies (epoxy, cloth, cutters, mixing materials, flox, micro, etc) Of course this can wait until much later in the build.,
- Static vents if using something other than Van's rivet method
- Something to mark off torqued bolts (ie Torque Seal but nail polish will do)