5e Crunchy House Rules.

Hit Points and Healing

• Short Rest = 8 hours of sleep and minimal activity, after which PCs can expend hit dice (if available) to regain hit points.
• Long Rest = 1 week of down time, no strenuous travel, no combat, after which PCs regain all hitpoints and hitdice

Combat

• Role individual initiatives each round
• Speed Factor for inititative (5e DMG p. 271 spells can be changed after initiative roll, but must be of lower spell level
• PCs can modifiy their intiative-rolled action to disengage, dodge, or dash with no penalty
• PCs can modify their initiave-rolled spell, but only to a spell of a lower (not equal) level, the new spell must not require material components, and they will cast last in initiative order.

Spells and Special Abilities

• Wizards can use *Advanced* Arcane Recovery (5e PHB, p. 115) and can regain spells slots equal to their wizard level (note: standard PHB rule is half wizard level) after 8 hours rest and spell study (House Rules Short Rest). For example, a 5th level wizard can regain one 3rd and one 2nd level spell, or five 1st level spells, etc.
• Druids
• Barbarians can use their Rage feature as stated in RAW, but applying our Gritty Realism time frames (e.g., Long Rest is one week).
• Clerics can use the equivalent of Arcane Recovery (5e PHB, p. 115) and can regain spell slots equal to half their cleric level (rounded up) after 8 hours of rest and prayer (House Rules Short Rest). Channel Divinity is rechargd after a House Rules Short Rest and Domain abilities are recharged as stated in RAW, but applying our Gritty Realism time frames.
• Bards can use the equivalent of Arcane Recovery (5e PHB, p. 115) and can regain spell slots equal to half their bard level (rounded up) after 8 hours of rest and study (House Rules Short Rest). Bardic Inspiration dies are regained as RAW, bu applying our Gritty Realism time frames.
• Paladins regain special abilities such as Divine Sense, Lay on Hands and Channel Divinity according to the House Rules Short and Long Rests. For example, when a Paladin finishes a long rest (1 week), they regain their expended divine senses. Paladins can use normal Arcane Recovery as a Wizard.
• Monks 

Experience Points

• Experience points (XP) are awarded for Combat, Exploration, and Social Interaction and divided evenly amongst the PCs, unless special circumstances prevail
• NPCs normally are not normally awarded XP for any of the D&D pillars, unless special circumstances prevail.