These two staples belong in every fly fisherman's vest or pack.
Mucilin – floatant
Apply to sighters and leader butt section for greased line methods. The green tub contains silicone and works better.
Loon Snake River Mud – “sinket”
Especially useful for light tippets and light sinking flies. Apply to leader below sighter or heavier sections, will degrease leader to eliminate surface tension effects and add effective mass for sinking. An effective substitute is river mud. I saw a tv show one time and Dave Whitlock was discussing the use of river mud to remove smell from flies also.