Asbestos heat mat, 2 wrenches, solder, bending spring, hacksaw, wire wool, copper pipe, to name just a few reasons.
Hardly ever need - heat mat (an old tile will suffice if absolutely necessary), hacksaw (what do you intend to cut the plastic pipe with, unless you're going to buy a plastic pipe cutter?)
Don't need solder if you use integral ring fittings for a few pennies more. And a tub of flux will set you back a fiver.
A bundle of 20m of copper would probably be enough to do the job for about £35 (about £10 more than the same length of plastic), and copper fittings are cheaper that plastic, so the cost won't differ by such a huge amount. A plumber would probably buy any surplus pipe from you.
Don't need a bending spring either if you fill the pipe with sand before you try to bend over your knee.
Why do you need 2 new wrenches? What do you intend to tighten up the shower, tap and radiator with?
So you don't need wire wool to clean the chrome off the the rad tails? You'll never get it right with a file unless you intend to solder.
Anyway, it's all irrelevant since you seem pretty happy with using speedfit. It's a matter of preference and confidence in the materials being used. Just remember to use pipe inserts, silicon spray to help get the joints fully in, and clip the pipes properly to stop them flapping around. Ideally, you should pressure test your pipework before connecting up to water, but this will involve you buying something to do so, which, like you say, isn't something you're likely to use often. Although you could get some money back by e-baying it (bit like that other stuff you're not going to buy
) Finally, remember to flush all pipework through before connecting anything sensitive like a shower mixer.
Am sure it'll be fine for a while. Don't be offended by me - it's not your doing it that I'm on about, we all have to learn from scratch. Hope it goes well.