Reddit mentions of Osborn 83112SP Economy Small Cleaning Stainless Brass Scratch Brush, 3/8" Brush Area Width, 7-1/4" Overall Length

I had to break this into another comment due to per comment character limits.

The following previously belonged to the above comment, but was moved here due to the above mentioned limts.

> Something you can do now: Build a filament drybox. Seriously, some filaments such as certain Nylons can go bad in just a few hours, depending on ambient humidity levels. All filaments are susceptible to moisture absorption, and ideally should be kept in something like a Spannerhands holder, even while printing, but at worst you should store them in a big plastic tub with silica gel beads to keep them dry.

> If I had to give one last tip, don't stock up on too much filament yet! Seriously! I thought I would be printing mostly in PLA but now that I've had a few weeks to work with it, I've learned I prefer PETG more, and now I have so much extra PLA! I'm sure I'll find something to do with it, but for my final tip I would add "And get a good variety!". Services like MakerBox (referral) let you try a bunch of different filaments on the cheap. It's not a ton of each filament (about 50g), but I love the variety of materials and colors.

Original second level comment begins:

Final Tips: Bonus Round!

1. Extruder Indicators are pretty cool (and USEFUL). You can get the magnets super cheap (or amazon).
   
2. Learn how to do An Atomic Pull (AKA Cold Pull), and learn it well. Do this every time you switch filaments (See "Doing it the lazy way" at the bottom of the page). You'll help remove built up deposits each time, which will help ensure a long, jam free life for you nozzle. This also skips the bleeding necessary when switching filaments (on your next "Load" you'll get a few mm of old filament and then pretty much pure new filament after that, instead of the 100mm or so of transition). You can skip doing a proper Cold Pull if you're using a brand new printer anyway. Just do a lazy pull each time you switch filaments, and then a proper Cold Pull maybe every 100 print hours, or after using extremely difficult (wet or super exotic) filaments to help remove any residue that may cause future jams or other issues. This does require undoing and redoing the idler tension again, but once you've done it a few times you can do the whole pull and filament swap in under a minute (minus hotend heatup/cooldown time). White Nylon is great for proper Cold Pulls, partially because you can crank the temp up very high (which ensures any residual filament in the hot end should also melt), White PLA would be okay for example, but may not properly pull PETG or ABS from the nozzle. White is great thanks to the color, of course, which allows you to see any residue easier; However, any color may be used. If you only ever use PLA, then PLA would be just fine for a Cold Pull. Seriously though, start by doing Cold Pulls from Day 1 and you'll easily cut out 50% of your future issues.
   
3. The small metric fasteners used in the printer are cheap. They are used in a lot of designs found online, so you should stock up (alternate source). The primary fasteners used are M3 Socket Head Cap 0.5 pitch, mostly full thread. You can also get the nuts very cheap. Square, Nyloc, and Hex. I can get the exact lengths used in the Mk3 if anyone needs them, though I'm not sure the exact grade used, it only really effects corrosion resistance.
   
4. You can also Calibrate the Extruder steps/mm and extrusion multiplier. Many people will tell you only the later is necessary but I prefer to do both anyway. Theoretically it does make a difference, but practically you can just compensate for steps/mm with the extrusion multiplier, and for all intents and purposes the result is the same, so "many people" are totally right.
   
5. You can also Calibrate the PID. You probably won't have to do this for PLA out of the box, but may find you have some temperature swings with PETG or ABS temperatures. The Official Help Article also discusses this method and how to calibrate using the LCD if you prefer. I like to keep my Mk3 settings vanilla (I've never used an M500 directly, and avoid them when I can), so I like to get my PID values manually and set them in my start GCode instead, which also allows me to setup my slicer so each switching filaments automatically switches PID profiles. The bed can be calibrated as well, but again you probably won't need to do this unless you're experiencing temperature swings more than -/+ 5°. One or two degree dips/spikes is perfectly normal (though theoretically can be tuned out, requires proper enclosure for stable ambient temps, etc).
   
   There are tons of other accessories you can get ahead of time. None of these are necessary, but are small things you might end up using (or wanting to try :P), and should help get you started getting a wishlist together. Besides the ones mentioned in this comment (and the one that precedes it) already:
   
   

• Wire Snips beat the included pliers hands down. For $4 how are you not going to pick these up right now? The cutting edge on a pair of pliers sucks and it doesn't help that it's ****ing halfway down the length of the tool. I tried to get away with just using the included tools and simply gave up trying to use the included pliers to cut zip ties. If you have Prime, get a pair of these now. Get a pair even if you don't - they're worth the shipping cost too. Thank me later.
  
• 608 bearings (for prints such as TUSH),
  
• Loctite 222 (helps prevent screws from vibrating free, not necessary thanks to Nylocs used in Mk3),
  
• A humidity sensor (for filament dry box and checking ambient),
  
• An accurate scale (for calculating remaining filament),
  
• A small fan (enhanced print cooling when needed (not very necessary except for ultra extreme bridges), enhanced circulation in filament dry box),
  
• Small bags (for silica beads),
  
• PTFE tube and matching Bowden Couplers (for something like Spannerhands),
  
• Lubit-8 (for the LMU88 bearings),
  
• SuperLube (Silicone Grease w/ PTFE for Bondtech Extruder gear maintenance),
  
• Canola Oil (for lubricating/cleaning filament and seasoning the nozzle/hotend (not necessary with modern hotends)),
  
• Small Brass Brush (also for Bondtech Extruder gear maintenance),
  
• Nozzle Reams (for the extremely rare jam, because you're doing your Atomic Pulls, right?),
  
• Extra Nozzles (no need for the kit, just an example. Hardened nozzles (black) are a good idea for composites, last longer than Brass, regardless of filament used. Prusa Mk3 comes with 0.4mm nozzle preinstalled, but you can easily swap the nozzle),
  
• E3D Hotend Sock (helps lock in heat for (theoretically?) lower current usage and more stable temperatures, also helps keep plastic off the heat block in case of print failure),
  
• Magigoo (or other adhesion aids) (for certain exotic filaments, otherwise not necessary with Mk3),
  
• Tempered Glass or Borosilicate printbeds (for certain exotic filaments),
  
• And of course, Isopropyl Alcohol (70% or better, preferably 91% or better) and Acetone, just to name a few...
  
  Edit: Upon rereading my comment I realized I have a problem.. I own every product I just listed..
  
  ^^Except ^^for ^^the ^^nozzles ^^kit ^^so ^^it's ^^not ^^that ^^big ^^of ^^a ^^problem, ^^right?... ^^Right?!

> I'm also wondering if a brass brush might be a handy thing to clean filament off any nozzle?

Those work fairly well - use one myself