I plan to carry some extra items like cables, spokes etc. What happens if I need to replace a cable? Should I carry a heavy cable cutter or just wrap up the excess until I find a bike shop?

I think you answered your question. I have in the past carried a small pair of pliers that weighted about 85 grams and had side cutters. I seem to remember them being useful, but it escapes me as to what I did with them?

So just wrap up the excess?

I carry a leatherman mini tool with pliers and wire cutters. It works pretty well but you can just tie off the extra length until you come to the next garage.
I used to carry a pair of needle nosed pliers which were quite handy.

That's what I would do, just tie it on somewhere out of the way.

Ditto on the leatherman, in addition to a mini tool, and a small crescent, and a spoke wrench.

Have the spoke wrench, I have a leatherman knock off that I already plan to bring on the ride. My multi tool has a spoke wrench and Allan keys. I will probably carry extra Allan wrenches as the ones on the multi tool don't have much reach.

Someone wrote once that a spoke wrench is the cheapest and quickest way to put your bike out of commission that there is. Learn to use it before you need it!

I don't carry all those "multi-weights" because they are heavy and often poorly suited to the job. Take an inventory of exactly what size hexes, etc. that you need and only carry them. Often the multi-tools are too fat to work well in tight spots and you can't expect to get much leverage on say a 6mm hex with a 2" throw. Try tightening up a crank with a Topeak Alien.

once I used a pair of toenail nippers.....they were not much good for toenails afterwards but they did get the job done...I now carry a mini-leatherman...that has been useful for many tasks

If need be, you can buy a pair of diagonal cutters in any hardware store. You could also probably get someone at a garage to cut the cable for free. You don't need special cable cutters to trim the end of a bike cable.

I learned the hard way (but not on my bike fortunately) to cut off the unneeded end of one of those cables that has two different heads before leaving home. (does that make sense - I mean on of these: https://www.rei.com/online/store/Prod...jpg&view=large)

Take a look at the small Vise-grips that are available. A Vice-grip tool is a useful emergency tool that can deal with rounded or frozen fasteners, act as a clamping device to hold broken parts together, and cut cables better then any Leatherman or multi tool. Down by the pivot of the jaws is a small anvil and blade cutter that snips cables cleanly and easily.