Came up with this for my own use and thought it might be of use to other folks.

Aasimar

• Add Necrotic and Radiant resistance
• Add Darkvision 60 ft.
• Change some of its damage to Necrotic or Radiant
• Add trait:
  Light. The aasimar sheds Bright Light in a 10-foot radius and Dim Light for an additional 10 feet. As a Bonus Action, the creature can suppress this light or cause it to return. The light winks out if the creature dies.

Dragonborn

• Add resistance from ancestry
• Add Darkvision 60 ft.
• Add action (with damage type for ancestry and increase damage and DC for higher CRs):
  Breath Weapon (Recharge 5-6). Dexterity Saving Throw: DC 13, creatures within a 15-foot Cone or 30-foot Line that is 5 feet wide. Failure: 5 (1d10) Fire damage. Success: Half damage.
• If the stat block has multiattack, add: One attack may be replaced with Breath Weapon.

Dwarf

• Add Poison resistance
• Add Darkvision 120 ft. and Tremorsense 60 ft.
• Add trait:
  Dwarven Resistance. The dwarf has Advantage on saving throws it makes to avoid or end the Poisoned condition.

Elf

• Add Darkvision 60 ft. (or 120 ft. for drow)
• Add trait:
  Fey Ancestry. The elf has Advantage on saving throws it makes to avoid or end the Charmed condition, and magic can’t put it to sleep.
• Add action (CR 3 and CR 5 get the extra spells):
  Spellcasting. The elf casts one of the following spells, requiring no Material components and using {ability} as the spellcasting ability (spell save DC XX):
• Drow:
  At Will: Dancing Lights
  1/Day Each: Faerie Fire, Darkness 
• High elf:
  At Will: Prestidigitation
  1/Day: Detect Magic
• Wood elf:
  At Will: Druidcraft
  1/Day Each: Longstrider, Pass Without Trace
• Add bonus action for high elves CR 5 or above:
  Misty Step. The elf casts Misty Step, using the same spellcasting ability as Spellcasting.

Gnome

• Add Darkvision 60 ft.
• Add +5 to Intelligence, Wisdom, and Charisma saves
• Add action:
  Spellcasting. The gnome casts one of the following spells, requiring no Material components and using {ability} as the spellcasting ability (spell save DC XX):
• Forest gnome:
  At Will: Minor Illusion
  2/Day: Speak with Animals
• Rock gnome:
  At Will: Mending, Prestidigitation

Goliath

• Change walk speed to 35 ft.
• Add trait:
  Powerful Build. The goliath has Advantage on any ability check to end the Grappled condition.
• For cloud goliath, add bonus action:
  Cloud’s Jaunt (2/Day). The goliath magically teleports up to 30 feet to an unoccupied space it can see.
• For fire goliath, change some of its damage to Fire. 
• For frost goliath, change some of its damage to Cold and add “and its Speed is reduced by 10 feet until the start of the goliath’s next turn.”
• For hill goliath, add to attacks “If the target is a Large or smaller creature, it has the Prone condition.”
• For stone goliath, add reaction (adjusting for Constitution modifier):
  Stone’s Endurance (2/Day). Trigger: The goliath takes damage. Response: The damage is reduced by (1d12).
• For storm goliath, add reaction (adjust damage to fit CR):
  Storm’s Thunder (2/Day). Trigger: The goliath takes damage from a creature within 60 feet of it. Response: The creature takes 4 (1d8) Thunder damage.

Halfling

• Add traits:
  Brave. The halfling has Advantage on saving throws they make to avoid or end the [condition]Frightened[/conditions] condition.
  Halfling Nimbleness. The halfling can move through the space of any Medium or larger creature, but can’t stop in the same space.
  Naturally Stealthy. The halfling can take the Hide action even when obscured only by a Medium or larger creature.

Human

• No changes required

Orc

• Add Darkvision 120 ft.
• Add bonus action:
  Adrenaline Rush. The orc takes the Dash action.

Tiefling

• Add Poison, Necrotic, or Fire resistance
• Add Darkvision 60 ft.
• Add action:
  Spellcasting. The tiefling casts one of the following spells, requiring no Material components and using {ability} as the spellcasting ability (spell save DC XX):
• Abyssal:
  At Will: Thaumaturgy, Poison Spray
  1/Day Each: Ray of Sickness, Hold Person
• Chthonic:
  At Will: Thaumaturgy, Chill Touch
  1/Day Each: False Life, Ray of Enfeeblement
• Infernal:
  At Will: Thaumaturgy, Fire Bolt
  1/Day: Darkness
• Add reaction for infernal tieflings:
  Hellish Rebuke. The tiefling casts Hellish Rebuke in response to that spell’s trigger, using the same spellcasting ability as Spellcasting.