Essential? To me; that means:
Ingredients:
-- PG
-- VG
--Nicotine
(first three can be in combination, or separate ingredients)
-- One or more flavor concentrates
A means to measure ingredients:
-- Small assortment of syringes and blunt-tipped needles
or
-- A scale that has 0.01g resolution
----- if using a scale, without syringes, may need an additional means of dispensing concentrates that don't come in dropper-tipped bottles. Disposable/reusable pipettes, syringes, disposable/reusable eye droppers, or extra dropper-tipped bottles all solve the problem.
Something to mix ingredients in:
-- Can be re-purposed bottles from commercially bought e-liquids
and/or
-- New bottles
A means to calculate the amount of ingredients to use:
-- Paper and pencil
or
-- Pocket calculator
or
-- E-liquid calculator (can be on-line, or down-loadable)
A work area that provides ample room to work, and is safely away from children, pets, and distractions... preferably with running water handy.
Time
Trying to mix, when one is in a rush, is a recipe for only failure. Time is also an e-liquid recipe's best/most consistent ally.
A reasonable supply of ready-to-vape e-liquid on hand:
The panic, and rush, to get something vapeable "right now;" can cause a mixer to cut corners, forget steps and/or ingredients, and be forced to vape unvapeable e-liquid. Having an adequate supply of juice, that is enjoyable to vape (commercial, and/or previous DIY), removes this added pressure to succeed immediately.
A means to record your work:
-- Paper and pencil
-- Spreadsheet/word processing software
-- (within) Certain e-liquid calculators
The manner of recording notes doesn't matter. What matters, is that it is something the user will use, and then uses it. Notes are essential for recording recipe ideas, what does/doesn't work, and what might want to be done differently next time.
Nothing is more heartbreaking than to mix up the genuine "perfect mix," only to not remember what was done, and never be able to repeat it. Notes are also a good tool to avoid repeating past mistakes.
That's my list of essentials. For me, everything else becomes a matter of convenience. As an old(er) guy, with crappy eyes and shaky hands; I do find the following nearly essential.
-- A digital scale became essential for me; because I couldn't see the tiny graduation marks on the smaller syringes.
-- A secondary large-mouthed primary mixing vessel (beakers, in my case); because my shaky hands kept missing the tiny-mouthed e-liquid bottles.
-- A small funnel to transfer my mixes from the beakers to the bottles; again, shaky hands.
-- A small hobby paint mixer; because I am lazy, and hated shaking all the bottles.
I have tried a bunch of additional tools, tricks, and and gimmicks; but none have lasted the long haul, for me. Others, I'm sure, have had different experiences; and those are every bit as valid, as my own.
That is the beauty of DIY; taking a basic process, and making it your own. Successful mixers, that I have known, all have a few things in common:
-- they find a way to keep it fun, so they want to keep doing it.
-- they are willing to fail. Mixing a bad batch (or 3, or 10) is not the end of the world. They keep trying different things.
-- they are willing to learn from their mistakes. They don't say this tastes nasty and give up. Instead, they try to figure out why it tastes nasty. Instead of looking at a bad batch as a failure; they are more likely to look at it as a puzzle to be figured out. For some, it can even be a motivator.
Those who most commonly fail as DIYers are:
-- The ones that have no time (family, commitments, good old "life"). (This is no fault of the individual; it just isn't the right time to embark on DIY.)
-- Those who don't have the have the patience to learn from their mistakes; and change their thinking and processes. The "Veruca Salt's" of the world generally don't do well with DIY.
(Everybody sing "I want it now!")
-- Those who "know it all". Those who think they have it all figured out... before they ever start mixing. These folks tend to think in terms of "this is how it should be," instead of thinking "this is how it is... what do I do next?" They will blame everything but themselves and their understanding and expectations; and usually give up out of frustration.
-- Those expecting to be professionally successful/profitable mixers right out of the gate. Unless they are living in a part of the world, that bans access to commercial completion, that is unlikely to happen. They don't understand the time, effort, and experience required, to turn out consistently good juice.
