Gaseous Form: Your ultimate get-out-of-jail card. Turn into a silvery cloud and float away. Immune to damage, spells, mind control- as long as there isn’t a gust of wind you are fine. True you leave your gear behind, which could be crippling at higher levels, but it’s better than tearing up your LV 18 fighter and starting over.
When the cleric is busy healing somebody else, with the thief nowhere to be seen, and the wizard out of spells, you better have the following potions ready to pull from your adventuring belt…
Healing: Cure light, medium, or serious wounds- based on your level and hit points, it’s always a good idea to bring-your-own healing for those times the cleric or paladin isn’t around. Even fighter-class characters with lots of hit points can suddenly drop half or more against some of the stronger and more cunning beasts in the monster manual so BYOH.
Invisibility: At lower levels this is your emergency escape plan, and even at the higher levels where encounters might still detect you going dark will at least allow you to escape or get in a better position to attack. Usually the wizzy hads this spell out in mass, but that takes a few game rounds and said wizard needs to be alive or not silenced.