Regular Airsoft temptations to avoid!

Regular airsofters are unlikely to fall for the "tourist traps" described in the "Backyard" section (but I did). Yet there are still plenty of things out there that will eat away your airsoft budget without contributing much to your field experience or will simply collect dust in some closet. Having less gear means less time unpacking and more time playing/socializing.
Think twice before:
Buying internal gearbox upgrades in individual boxes: pistons, bushings, shims, compression rings, spring guides, air nozzles, gearbox shells etc. There are a lot of good after market upgrade parts out there. If you start to pick and choose parts inside your gearbox, the markup and shipping will cost you dearly. Double check with your local airsoft repair enthusiast or the airsoft shop of your choice to ensure they will upgrade your brand of AEGs. Some AEGs have nasty quirks when it comes to the internals and the gearbox
Save money by looking at brand name complete tune up kits or lower cost tune up Kits (Ex: Guarder or Hurricane)
Avoid DIY (do it yourself) internal gearbox upgrades or "repairs", even if your gun breaks. Not only are gearboxes hard to open and put back together, the internals require a lot of TLC (tender loving care) to function reliably (for example the shimming operation). Putting the spring back can be a hassle.

You will be able to take your gun apart and replace the inner barrel and hopup unit yourself, just dont touch the gearbox : )
Save hours of headache and money by paying a small fee to have your guns upgraded by a professional (preferably locally)
8 cell (9.6 volt batteries) - These will often not fit in your weapon and will require an external battery pouch. Buy a high mAh 7 cell battery (8.4 Volts)
Be skeptical of high FPS but cheap AEG. This most likely means that someone swapped the stock spring to something more stiff to get the gun to the 380, 400 or 450 FPS range. Expect a host of mechanical problems down the line. I would not trust a 400 FPS gun, unless tuned up and upgraded by an expert.  450 FPS fully automatic guns are prohibited at most fields.
Get a stock AEG and upgrade it later. Alternatively, purchase the upgrade service offered by your airsoft retailer.
Many people are tempted to get a Personal Defense Weapon (PDW) like MP5K or an MP7 as a backup (same goes for an Uzi or a Scorpion if you feel like a badass). The cost of these is comparable to getting a second AEG (extra mags, sling/holster, etc). The performance of these PDWs is decent, but not as good as an AEG. If you truly consider getting a PDW, look for one on Ebay/Craigslist or your local airsoft forum. Chances are someone has one for sale for 60 % of what you would pay at most retailers.
Save money by getting an AEP or a GBB pistol as a backup.
Stay away from expensive military gear or replica gear as a beginner airsofter. Find out of you like the sport first before making major investments in gear or attempting to sumulate some real world military unit. Save money and go milsim after you see the limits of airsoft.
Night vision or night vision scopes. These are very expensive, even if you get Generation 1 type off ebay. There are 2 types: infrared illuminators and existing light intensifiers. Infrared illuminators have limited range and make you visible to other players using the same technology. Avoid the temptation of getting these for a single game.
Save money by counting the number of night games you will attend before ordering these.
Cheap Helmet or Gun mounted cameras. While having airsoft video is cool, as you may notice, most airsoft footage on youtube lacks the depth of view and the video quality makes it difficult to see who you are engaging. There's plenty of used  cameras on ebay.
Read reviews and google for examples of footage from your camera before buying. Look specifically for airsoft footage.
Airsofters in general do not wear helmets and opt out for other methods of head protection, because helmets are often too cumbersome (interfere with goggles) or hot.  Save money on a helmet(30-80$)
Save 10$ on cheap baklava replicas, (or underarmor replicas).If you decide to get one for head/face protection, get one that can really wick moisture away from your head and keep you cool. Skiing masks (5$) are extremely hot when used with goggles, even in the middle of winter, don’t pick up one, even though it is cheap. A shemagh (olive or tan, 10$) works well during the colder months and can make playing even in the freezing rain decently comfortable.
Get a good Baklava instead
Elbow Pads. These are rarely used and may be uncomfortable to wear. The only time when they are useful is when prone on a wet floor. You probably wont wear them after 1-2 games. Save 10-20$
Avoid cheap electric box magazines. The only place where a Box/drum magazine looks acceptable is an M249 or an RPK. An electric box magazine has a pressure switch which winds up your magazine so you don’t have to. They are difficult to manage and make noise. A TM high cap for AK 47 series comes with a hex key that allows you to rapidly wind up your highcap in combat, turning your AK into a support weapon.
Save yourself 100$ or at least read/ see a review of a box mag that you are about to purchase
Evaluate your need for a tracer unit (100$) and glow in the dark BBs (15$/bag). Night games are pretty rare (mostly scenario games). Tracers do look very cool though and also produce a muzzle flash. Count the number of night games that you are expecting to attend before buying
Save money on LED Flashlights and tactical flashlight imitations. It does not matter how many LEDs a flashlight has, unless there's a good focusing lens, the light diffuses after ~40 feet and you cannot see much past that point at night. This makes you a fat juicy target. The only place where such flashlight will be good is in a poorly lit indoor CQB facility.
Get a good focused flashlight for night games.
Laser sights. While they look cool on weapons, ask people if they have actually used them to aim during airsoft games, and the answer would be "No". The players on the "receiving" end of the laser complain about them quite vocally, resulting in laser sights being rather useless for airsoft purposes. Save yourself 10$-140$ on a laser sight, as you wont use it much. White BBs act as tracers anyway. 
Bipods. There's no need for a bipod to shoot at targets less than 200 feet away. The fast nature of most airsoft engagements will have you shifting firing directions multiple times per engagement. The only place where a bipod may be needed is for heavy machine gun replicas or sniper rifles.
Save 10-100$ on a bipod or buy a used one
Save money on Urban(snowflage) or any camouflage with white, because it stands out like sore thumb in the woods and defeats the purpose of camouflage. ACUs may also be too bright to wear in the woods, observe a few people who wear them to airsoft games before deciding if this is the camo for you.
Save money on white camouflage and go with Woodland or Desert patterns instead.
You can also save money on overpriced camo. The internet made it available to get camouflage BDUs in almost any pattern available out there. Unfortunately, importing authentic military uniforms is expensive, and the differences between most woodland camouflage patterns at engagement distances of ~300 feet are negligible. Remember, most airsoft players are civilians, wearing goggles/masks, they are not optically assisted military observers, marksmen or snipers (who can notice differences in camouflage) or pick out an out-of-place camo pattern.  Save money by sticking to 1-2 sets of camouflage.