Bonus Actions

In addition to all RAW uses of bonus actions, here are some more. Some require a skill roll.
Change initiative: roll D6, add or subtract the result from your initiative position, effective next round. If you tie another character's initiative, you choose how to resolve the tie.
Fending attack: roll D6, subtract the result from the to hit roll(s) of your next melee attack action. Target(s) successfully hit with your modified to hit rolls also apply the D6 result in their next attack roll made until the beginning of the next round.
Toss a potion: successfully toss a potion (or something similar) D6+Dex mod squares to a targeted ally. If the roll is not enough to match the range to the targeted ally, it falls short and may break.
Wild swing: roll D6, subtract the result from the to hit roll(s) of the next attack action, & add the result to the damage roll of the wild swing. Regardless of the number of targets, only roll one D6 and apply it to all targets of that attack. Can only be applied to attacks that use to hit rolls.
To use these new combat skill checks roll your skill vs DC = opposed creature's skill+10.
Induce fear; Intimidate vs intimidate. Success applies a d4 Bane effect for one round. This is a fear effect, so creatures resistant to fear gain +10 on the DC; those immune to fear are immune to this effect.
Feint; Deception vs Insight. Success grants +2 to hit target with your next melee attack this round.
Push; Athletics vs Athletics. DC +5 vs targets one size larger; impossible vs targets two sizes larger. Success pushes target 5'.
Knock offbalance; Athletics vs Acrobatics. Success reduce target's AC by 2 until the beginning of their next turn.
Creature Knowledge Check; [varies] vs DC 15. Success grants insights into creature's strengths, weaknesses, & abilities. The skill used depends on the creature type:

• Arcana -> Aberrations, Constructs, Dragons, Elementals
• History -> Giants, Humanoids
• Nature -> Beasts, Fey, Monstrosities, Plants, Oozes
• Religion -> Celestials, Fiends, Undead

Use terrain; [varies], often Athletics or Acrobatics. DC varies, usually 10 to 15. Success grants advantage on your next attack this round - failure results in disadvantage instead. "Can I leap off the bookcase onto the Ogre's back?" "Yes, roll acrobatics DC 13 for advantage."