[RPG] What are all the published objects that require the Use an Object action?

This is the answer that you want to read.*

For this list I have compiled all objects that specify that they take an action to use. This list excludes magical items and objects that don't explicitly state that they take an action to use (like tools and objects that require an ability check instead, etc.).

Use an Object

You normally interact with an object while doing something else, such as when you draw a sword as part of an attack. When an object requires your action for its use, you take the Use an Object action. This action is also useful when you want to interact with more than one object on your turn.

This makes it distinct that all normal interaction that doesn't require an action is handled by Other Activity on Your Turn (PHB 190) and similar sections in the rules. Note that "useful" doesn't mean that you can use objects that don't require an action for the Use an Object action.

Other Activity on Your Turn (PHB 190):

Your turn can include a variety of flourishes that require neither your action nor your move.

If you want to interact with a second object, you need to use your action. Some magic items and other special objects always require an action to use, as stated in their descriptions.

See here that you can use your action to interact with a second action, but that that action is distinct from the Use an Object action which is for objects that require your action.

Activating an Item (DMG 141):

Activating some magic items requires a user to do something special, such as holding the item and uttering a command word. The description of each item category or individual item details how an item is activated. Certain items use one or more of the following rules for their activation. If an item requires an action to activate, that action isn't a function of the Use an Item action, so a feature such as the rogue's Fast Hands can't be used to activate the item.

The thereby excluded magical item actions are definitive all magical items with the properties: Command Word, Consumables, Spells and Charges. A very well-versed rules lawyer could argue that all other magic item actions fall under the Use an Object action because the kind of property of activation is defined by these four terms. For the sake of sanity, I will exclude all magical items, even those that may be lawyered into the eligible pool for the Use an Object action. I wouldn't allow this lawyering anyway.

Fast Hands (PHB 97):

Starting at 3rd level, you can use the bonus action granted by your Cunning Action to make a Dexterity (Sleight of Hand) check, use your thieves’ tools to disarm a trap or open a lock, or take the Use an Object action.

The list:

Ball Bearings (bag of 1,000)

Bomb

Caltrops (bag of 20)

Climber's Kit

Dynamite (Stick)

Grenade Launcher

Grenade, Fragmentation

Grenade, Smoke

Healer's Kit

Hunting Trap

Lantern, Hooded

Poison, Basic (vial)

Tangler Grenade

Tinderbox

Things that notably aren't on the list:

Acid (vial), Alchemist's Fire (flask), Holy Water (flask) and Oil (flask) as an action all four require you to make a ranged attack. Oil (flask) is an outliner because it specifies that you can pour it on the ground (but not that this takes an action). At your discretion, you may add these four to the list.

All ranged firearm weapons that have the Reload property can be reloaded, and you may use the Use an Object action for reloading (DMG 267):

Reload. A limited number of shots can be made with a weapon that has the reload property. A character must then reload it using an action or a bonus action (the character's choice).

All poisons other than the Poison, Basic (vial) don't specify that applying the poison takes an action.

All explosives, firearms and alien technologies are part of the DMGs Workshop and therefore optional content.

_{* Except for magical items that may be lawyered to fall under the Use an Object action.}