To make useful, non spell oriented gadgets with a tinker type artificer- net launcher, sleeping gas (poison type) grenade like things, auto retracting grapnel, etc. for a vigilante type crimefighter ish, probably with a dip in shadow monk or a monk dipping into artificer… there is no guideline for inventing useful stuff, must use a spell slot or it doesn’t work? Infuse a bag of holding into a belt compartment… wield versatile weapons… What do you think

I'd just use reflavoring for this kind of thing. Want the effect of grease and willing to spend a spell slot for it but want it to be a gadget? Just cast the spell and describe it as a grease gun or whatever. Cast sleep and call it a gas grenade, etc. All you're really doing is spending an action to make an effect. You get to describe what that looks like.

Now my question is which spell/infusion works the best as a handy can of shark repellant? 

As per the expanded rules for Tools published in Xanathar’s Guide:

Alchemist's Supplies can be used to create the following listed items: “Acid (vial), Alchemist's Fire (flask), Antitoxin,* Oil (flask), Perfume (vial), [and] Soap.”

While those are the example items listed, it would not be unreasonable for Alchemist’s Supplies to also be used in the creation of such other items as: Blasting Powder, a Block of Incense, a Bomb, Candles, Dynamite (Stick), Grenade, Smoke, Gunpowder, Ink (1 ounce bottle), Insect Repellent-Incense, Insect Repellent-Salve, Paper (one sheet), Sealing Wax, or a Tangler Grenade.

Quote from Kaboom979 >>

Now my question is which spell/infusion works the best as a handy can of shark repellant? 

 
Trident of Fish Command?

Quote from Kaboom979 >>

Now my question is which spell/infusion works the best as a handy can of shark repellant? 

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