What fasteners are triple squares? I've not done much work on my Golf but I've not seen one yet, or on any previous cars (Honda/Peugeots) are they a VAG specific thing?
I think so, never needed them before I got my first VW!
Steering wheel centre bolt for one (M12 from memory?) which is the reason I bought my complete cheap set of them, then my brother gave me his Facom ones as he got rid of his old VR6.
Halfords is a good place to start, but you will find that you need far more.
Another place to look believe it or not is your old mans shed - great place to find vintage good quality tools - or also try the many auto jumble events - I picked up a Mac impact gun for next to nothing and just needed a bit of oiling.
A decent length breaker (1/2" head) is a god send for stuck stuff, I use impact type sockets on the bigger stuff as they tend to come in 6 sided instead which gives a better fit on something that needs a lot of torque either to take it off or put it on and less likely to round off.
Then once you have got everything you need, think again because that's when upgrades kick in LOL. Gradually replacing some of my older cheap spanners with Bluepoint, Teng and Facom as I go. Already done all the screwdrivers with Wera stuff which is real nice - I have their mini wrench set and one of their Zyklop ratchets in 1/4".
Then comes air tools, better jack, axle stands are a must, a creeper - basically anything that makes the job easier if you start to tackle more and more stuff.
My most recent purchases are a low range torque wrench, Wera screwdrivers (standard type, as the ones with replaceable bits don't get into those deep seated screws in awkward places), upgrade my brake bleeder and currently on the hunt for a bigger air compressor as my Lidl one is just not up to spinning a good impact gun.
Not really a lot I can't tackle now with what I have in the garage - but I do all my own work that requires one off uses of expensive manufacturer specific tools.