99% of what I carry is unnecessary. Meaning: I don't typically use it. The remaining 1% is pretty much summed up as "water and snacks". I can't say I've ever really "needed" a whistle, signal mirror, firesteel, compass, etc. The compass I use, but not because of need so far - more so to keep in good practice with it. To an ultralight hiker ALL my gear is probably unnecessary. But to me it's essential and mandatory. Depends on how you look at things.

I have a pack that is too large to be considered a normal day pack ("Deuter Futura 32 liter" http://www.backpackgeartest.org/reviews/...20Chuck%20Kime/ ). But I load it lightly and wear it anyway. For me, it's much much much more comfortable understuffed than an overstuffed too-small pack.