Whilst we all love a good accessory, there's no question that the 'accessories' department of any good shop can end up becoming the home of all the weird and wonderful items that are hard to categorise.
Out of the hundreds of items, which ones are actually genuinely really useful and stand the test of time?
Over 20 years, I've used, lost and broken an awful lot of kit and these items are the ones that I think should be in every divers kit:
A Bolt Snap or Double Ender
Within the diving community there can be a strange attachment to boltsnaps (geddit) but why? The reason is simple, a spare double ended boltsnap can be used for a multitude of purposes. I just clip one off to one of my chest D rings and leave it there. I can use it if I suddenly find I need to clip something away: For example, a broken lanyard or clip on a torch or camera. In a bind it can be used to temporarily fix a broken buckle or even used as a tank banger to attract attention. I like to use at least a decent size one like a 120mm. Go on, it'll be the best tenner you ever spend (possibly).
A DIN Adaptor
If you own a DIN regulator then you need one of these. Yes, most tanks these days feature a modular valve but there are still parts of the world, like the US and the Caribbean, where tanks are A-clamp only. I've also experienced issues where a modular tank valve has an insert with a stripped allen key fitting and can't be removed. Having an adaptor in your dive bag may just save the day! Always take it off when you've finished though as if you leave it on, if might get stuck to the DIN wheel and then you just have a very large and ungainly A clamp regulator and you might cry.
A DIN Insert
At the other end of the scale, if you own an International/A-clamp regulator then you really need to have one of these. DIN has now overtaken A-clamp as the fitting of choice through most of Europe now and wherever you find a modular tank valve you'll discover that inserts have a habit of going walkies. Having your own DIN insert can sometimes be the difference between whether or not you're actually getting in the water so for £7 it's a no brainer.
Why wetnotes over a slate? Slates have limited space to write on, get messy over time and the pencils tend to get lost or snap off. Wetnotes will sit in a pocket, provide plenty of writing space and the pencil is protected inside. With wetnotes you can write stuff down and keep it for reference later (like a rude drawing to show your buddy on a safety stop).
360 Observe Mirror
Waterproof Ultima Dryglove System
Pandora O-ring set
It's all very well having one of those cute tank keyrings full of O rings but in my experience they never actually fit the thing you need it for. It's much better to have an organised set like this. It has a pick, christolube (O2 clean unlike silicone grease) and a range of all the useful O-rings you'll ever need in a bind from international ones for tanks, DIN ones for regs, the O-rings for LP and HP hoses and even the tiny HP swivel ones. A gem of a product.
Ceramic Line Cutter
You need a knife and you can knock yourself out debating over whether you need a blunt ended breadsaw or a lethal stilleto however every diver should also have a line cutter. In the real world you won't be fending off sharks or opening up abalone but on a bad day, you might get tangled in fishing line or need to cut someone out of their equipment. A line cutter is far more useful in these circumstances and because they're small they can be mounted in all sorts of places from computer straps to your BCD.
A Neptune III IDM and Comms
Stop it, you're being silly now; Steve