Q Tips (seems strange for me to automatically say q tips but most of you folks are from the USA and would probably get confused if i said cotton buds). Have to have these for cleaning decks. I'll switch out a wick most days and the entire base of my K4 will get stripped and washed. Q Tips are needed to clean the deck, juice wells etc. They just get into all the little nooks and crannys, chimney, chamber, everywhere that's to tiny to wipe down with paper towel.
Interdental brushes. I use these to clean around the air vent below the coil and might give the juice channels a once over now and then. They get rid of any potential build up of that tar like substance and keeps everything looking nice and clean.
Allen key. I switched out all of the existing deck screws for allen head screws. They make building coils so much easier.
Paper Towel (Here it's called "kitchen roll" but maybe you folks may not know what that is. I actually prefer paper towel). Use this everytime i open up a tank to re-wick etc. Also, do you know that thing when you've re-filled a tank, placed the juice bottle down, then see liquid somehow still seems to seep from the top of the nozzle. I always wipe all that off with paper towel.
Nail clippers. Always used these to snip kanthal.
Spare Juice Bottles. Went from 30ml to 50ml to 100ml.
Plastic Measuring Cylinders. For D.I.Y
Plastic mini Funnels. A must for D.I.Y. Always remembering that these don't work unless the bottle i'm filling is given a little "squeeze and release" just as the funnel nears full.
2ml syringes. For D.I.Y Flavourings. A lot more accurate than regular syringes and measuring cylinders i find.
Coil winding rods, Scissors, ummm ?.
Been meaning to get a little wire brush.