This pack will work in vanilla Minecraft, but for the best experience, use the following mods:
For connected textures on planks and bricks, as well as translucency on some blocks, use Optifine or Continuity
For performance, use Sodium (incompatible with Optifine)
For Lego-accurate flower placement, use the Centered Plants mod by Wisx

Plasticraft Premium requires the following mods:
Continuity for same reasons as above
Entity Model Features and Entity Texture Features for custom entity models
CIT Resewn for custom named weapons