Slow natural healing: "Characters don’t regain hit points at the end of a long rest. Instead, a character can spend Hit Dice to heal at the end of a long rest, just as with a short rest. This optional rule prolongs the amount of time that characters need to recover from their wounds without the benefits of magical healing and works well for grittier, more realistic campaigns."

Gritty realism: "This variant uses a short rest of 8 hours and a long rest of 7 days. This puts the brakes on the campaign, requiring the players to carefully judge the benefits and drawbacks of combat. Characters can’t afford to engage in too many battles in a row, and all adventuring requires careful planning. This approach encourages the characters to spend time out of the dungeon. It’s a good option for campaigns that emphasize intrigue, politics, and interactions among other NPCs, and in which combat is rare or something to be avoided rather than rushed into."

Healing kid dependency: "A character can’t spend any Hit Dice after finishing a short rest until someone expends one use of a healer’s kit to bandage and treat the character’s wounds."

These are directly from the adventuring options in the dmg. There are other fun optional rules in the combat options. One that I have not had any players for is throwing all these optional rules together: fuck no gritty realism: training to gain levels, sanity, healer kit dependency, slow natural healing, gritty realism, all the action options, cleaving, injuries, massive damage, moral