So there's this thing which seems awesome though I haven't tested it. And there's this thing that everyone probably knows about already. I love the idea of letting PCs avoid direct damage in exchange for losing something else. Because although death should be a real possibility, it's still the least interesting thing that can happen to the PC. Much more fun to prolong their agony a bit further.
So how's this for a houserule-upon-a-houserule: In a game using Matt Rundle's Item Tracker, whenever a PC is a) being attacked by an enemy as they're running away, b) being grappled by an enemy or c) any other escape-y type action that they can get the DM to accept, then they may sacrifice one of their item containers to guarantee their escape. The fireball roars behind you, but only burns your backpack; the tentacle reaches out to grab you, but only snags your bandolier; the wolf leaps as you climb to safety, and its jaws tear a hole in the bottom of your treasure sack.
With the following caveats:
1. The container that's lost is chosen at random.
2. The player's decision must be made before damage is rolled.
(Hopefully you will get situations like "I'm on 4hp and the bite does d6, but if I take it on my items then there's a 1/4 chance that it'll swallow my treasure sack..." "Yeah, but there's a 1/4 chance that it'll swallow your highly unstable explosives!")
3. If the attack requires a saving throw, then sacrificing your item gives you an automatic pass on the saving throw. That means you still take half damage from the fireball, etc.
4. Circumstance will dictate what exactly happens to your items, whether they are grabbed, dropped, incinerated, swallowed, transported to the birth of the universe, etc.
5. The same monster can't be fobbed off with an item sacrifice more than once. (Or, alternatively, you must make a DEX check for each sacrifice you want to make beyond the first.)