A. Ive heard everything from peppermint tea to the earwax of a tibetan yak!
You really need nothing but water. A healthy snake exudes all the natural oils needed to lubricate the old skin.
If your snake is having trouble shedding, the most likely bet is that your husbandry needs an overhall.
Your enclosures humidity levels are too low.
you can do several things to combat this, including, using a larger water bowl (larger surface area, not deeper) or moving the waterbowl closer to the heat source.
Having already encountered a difficult slough, there are a few tricks you can use to help.
1. Misting
spraying your snake and/or its enclosure will raise humidity, however this is a temporary measure.
2. soaking
giving your snake a swim in shallow tepid water in a tub or bathtub will soften the dried out skin allowing easier removal.
3. pillowcase
using damp (not wet) pillowcase, and allowing your snake to move about and rub itself inside for a hour or so, often does the trick.

NOTES: NEVER try to remove your snakes brills (eyecaps), this can cause damage to your snakes eyes. If in doubt, leave them intact, fix the humidity issue and they will be shed in the next cycle.