I use old army shoulder back as my day back. I usually keep in there:
Matches (water proof canteen or similar)
Leatherman Blast
Metal wire
Plastic wire
Zippo
Diamond Sharpener.
Fenix L1T v1 flashlight
1 folded garbage pack
2 folded regular plastic bags
3 assorted minigrips (they're handy)
Miniatury prying bar
Compass
First Aid kit (with space blanket)
Some paper in plastic bag
Water canteen (2nd canteen is in belt if possible)

Enough me to survive in case of emergency 24 hours in nature. I usually keep clothes that are 100% cotton or natural materials in summer and as much wool as possible in winter with as little as possible synthetics.

My small daypack weights approximately as much as Empty AK-47. I usually have my Dumpster Mutt with Bill Sigle mod on belt and ZT 0500 MUDD folder in pocket. Two good knives and good multi tool and skills I learned in army about survival.

I learned in army how little man can survive so I kinda became minimalist but last years I've think to add something nice to have.