Agree completely with Rob MacFarland. Can't speak to the mainsail slides since I only use the old fashioned slugs...of which I do always carry spares. Have often carried spare main, but not always. Spare spin poles: Yes! When I was dismasted, a spin pole was destroyed in the same event. Still had two that enabled me to rig a jury rig mast with 2 poles each secured to opposite toe rails with lines rigged fore and aft. Used small jibs hoisted with jib foot becoming the luff. Got me there.
In short, look at the things that "might" happen...aforementioned...and be prepared to cope with them. Remember the Boy Scout motto!