What are all of the ways to increase HP regen?

Solution 1:

The Constitution Wiki page includes the ways to increase health regeneration. I don't believe there are any other ways than what they have listed (I don't know of any at least).

First, the default regeneration rate is 0.1% of the players max Life Points level (rounded down) every six seconds. So, at 9900 Life Points, you will gain 9 points every 6 seconds.

Here are the boosts the Wiki lists:

Resting - Regenerates at a rate of 1% of the players total health per six seconds (stacks with the default rate as well ie at 99 Constitution, you will get 99 + 9 every 6 seconds).
Listening to a musician - Regenerates at a rate of 1% of the players total health per three seconds.
Rapid Heal Prayer - Still the default rate, but at every three seconds.
Rapid Renewal Prayer - Still the default rate, but at every 1.2 seconds.
A Regen Bracelet - Raises the default rate to 0.3% per six seconds.
The Regeneration Aura - Doubles the rate at which health regenerates (0.2% at six seconds) .
The Fortitude prayer - Stacks with the default regeneration - essentially doubles the rate (0.2% every six seconds).
The Dream Lunar Spell - This one is difficult to interpret from the Wiki, and I haven't done the quest needed to unlock the spell. According to it, it results in 100 life points per minute, making it 1.67 a second, or 10.02 (10) every 6 seconds.
The Constitution cape perk - Doubles the rate at which health regenerates. Stacks with fortitude. The perk can also be used with a max cape or a completionist cape.
Entering a bank - About 500 points per second.