I had a silly build using a Samurai with most feats going into Unconquerable Resolve (can also be done with a Kinetic Knight, as they get the Resolve class feature at lvl 3). Every time you use Resolve, you also gain 1 temp HP per HD, stacking with the number of times you've taken the feat. So if you went crazy with it (probably not optimal...), at level 9 as a Human Samurai, you could have taken the feat 6 times, giving you 9(HD)×6(feats)=54 temp HP at a minimum of 5 times per day. At 20, you could have 10 uses that each give 20x11=220 HP.
Resolve can be used as a standard action to remove conditions, and more importantly as an immediate action when dropped below zero HP to stabilize yourself.
Toss in the Yojimbo archetype so you can use your Resolve feature on others, and/or the Headband of Deathless Devotion to boost Resolve by 2 class levels.