Yes to the poncho - I've an integral designs one which is great as a waterproof when walking and as a shelter in a pinch. I think I'd be ok with that as my waterproof in my bag, and wouldn't feel it was a swizz as I carry it around daily. The shirt question is a good one. I often wear a t shirt with an open shirt over it, I've a nice second hand checked Rohan one. So I might feel ok about that.
I have a Germany army shirt, it's cotton, and quite a tight weave. I use it as a light coat during the summer, it would be what I would improvise a filter from. So your choice of shirt sounds about right.
So, based on what I've seen so far:
Cordage I could improvise,
The waterproof - poncho
So my five would be:
Crusader cup
Zippo (until I'm better at lighting)
Knife or Axe - though one of mates gave me a penknife thing which has an axe as part of the handle!
Sleeping bag
An item of food - I'm a bit stuck on what, I can't eat grains of any kind, or refined sugar, - it's a migraine thing, very effective in keeping migraine at bay but a bit of a pain.
Hmm, more thinking..
Yesterday Birchwood of this parish handed me her zippo to light my stove with, after a couple of minutes I through it back and asked for something else (we were sat 6 foot away, it was more a gentle pass...). Zippo's in my experience are not reliable, ditto most lighters. You would be better off playing with a ferro rod. It is also more likely to be within the spirit of the event.
The Knife cum axe cum survival tool. Without know which one it is, it's hard to say for sure, but in my experience anything like that is going to be pretty useless at everything. You are better off either having a decent axe, or a decent knife. Trying to combine both is just going to end in pain. If you wanted something more substantial than a knife, consider a Kukhri. Tho I doubt you'll find much a Mora clipper isn't good enough for. If you wanted to combine two multi use cutting tools into one item, then you are better off taking something like a SAK Farmer, the saw plus knife combo is likely to be more useful. A saw is likely to be more energy efficient.
As for the taking food. I am assuming the idea of such an activity is to survive for a period of time using your skills and the 5 items you've brought with you? You can forage for food, it's harder to forage for a bivvi bag or tarp or what ever extra item of kit you can think of. If I was going to have any food with me, I would most likely forget that I had those salt and pepper sachets in my pocket from the take away the other day... oops
.
If you can't eat grains anyway, don't worry, look for carbs. Making the assumption you're in the UK, this means Primrose and Cattails. Or you could go with the Atkins diet approach, and eat Dewi for that land rover door joke
Why carry food, when it can walk itself upto the moment you need it, and you can also then have his 4 things (don't bother taking the door from him
)
J