I have added a Helikon-Tex Swagman Roll to my kit at a cost of $125. Where I hike and camp the nighttime lows are generally around 35F to 40F even in the summer and I learned the hard way to carry a warm layer! It's basically a poncho/woobie kind of thing.

Most of the rest of the items I carry are relatively inexpensive. I do keep a $100 multi-tool and a $90 ESEE knife clipped to the exterior of my bag. I suppose they're "survival items" in a sense but they're just items I wind up needing often.
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“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman