Strong, flexible cordage has so many potential uses in an emergency, or daily life, that I always carry some in my HUMMER and bugout bag. It is possible to craft some from natural sources in the wild (in a true emergency) but you have to be in the right area, know what you're doing, and you'll expend a lot of time and calories doing it. Why not just carry some? It has little weight in small amounts and is reusable most of the time. There are a number of options here depending on quality and size.

I carry three types:

Parachute Cord (550). Be aware that parachute cord and paracord can be different. Sometimes paracord is a knock-off brand. Real, military-strength, parachute cord is very strong and has internal strings that can be used for smaller tasks. It's like carrying many cords in one small package. I carry at least 100 feet of it, cut in 25 feet lengths, and only cut it beyond that when absolutely necessary.

Catfish Bank Line. This is tarred twine in various test strengths. I usually carry light (#12) and heavy (#36) versions of this line. It doesn't smell the best but is great in wet conditions.

Small rope. Size is up to you, but I usually carry about 50 feet of 3/8 inch. Lot's of uses here.

Some of the possible uses of cordage:

Hanging pots over a fire
Boot laces
Making fire with a bow drill
Traps / snares
Fishing line
Early warning devices
Building shelters
Field dressing an animal
Lashing branches together (carrying wood or building a raft)
Rifle Sling
Preventing gear loss (tie it to yourself)
Making a net
Measuring time and distance
First Aid
Clothing repair
Tool repair
Loops for carrying gear
Wrapping tool handles
Retention lanyards
Improvised weapon construction
Rappelling and climbing
Belay cord for low visibility conditions
Securing doors