You can checkout my kit on the 'My Kit' Tab
Kit should be straight forwards... However, often the focus for kit is in the wrong direction... Rather than thinking can I get a jacket that's 50g lighter, should we instead be asking, 'Is this going to keep me warm and dry if I get stuck on a mountain?'
When you're out racing for a long time like in a 100 mile ultra, maybe even just a hilly trail marathon, you might experience some poor weather conditions. If your jacket is leaking and you've not slept all night and it's getting cold and your legs are tired but you've got all your kit on, it's very easy to get to a nice warm checkpoint and think 'Bugger it, I'm not going back out in that' as you begin to shiver at the thought of heading back into the cold night.
In reality you aren't injured or anything and physically could keep going but just the discomfort of plodding on in those conditions isn't a nice thought. You end up with a DNF because you took a poor quality jacket and skimped on kit. Perhaps the next people into the checkpoint are at least dry on the inside and heading back out into the rain they are at least shielded from the rain. An hour later the weather could brighten up and clear, maybe it will get worse, either way just having the right kit for the job can keep you in a race! It doesn't mean you need the most expensive fancy things, just something that is 'fit for purpose'
The other big point about kit is make sure you have practiced and are used to the kit you are going to use, don't turn up in new kit on the start line that you've never used. Eg I've met someone totally lost with a GPS in hand because they didn't know how to use it, I've seen some impressive cuts from a poorly fitting backpack grating at the skin all day and more posts online about foot problems than I could ever count.
After a while you should be able to dial down your kit and know exactly what you need so you can confidently turn up to the race knowing that you can handle what you're going to face without any panic or worry that everyone else is carrying something different to you.
See you on #5 for the next thing that'll go wrong on you one day, fuelling and nutrition for 100 mile ultras