One word: Spit!
It works remarkably well, and the great thing is that you don't have to spit a whole galoon into your FL, 2-3 spits works wonders. It has the same texture as a regular "Durex" and it has kept me and my STU busy during the evenings when i ran out of lube a month ago.
I myself produce a LOT of saliva when I'm mounting my STU, brings my thoughts to a dog humping wildly with his tongue hanging from th side of its mouth. So it's no big deal for me to "relube" by beauty!
All 100% natural pleasure (apart from the FL).