the intake and exhaust gaskets vary on different kits. some kits, as soon as you take off the intake or exhaust, the gaskets crumble into powder. there's some with thick, spongy exhaust gaskets that will never allow you to tighten the exhaust all the way, and then they'll burn up and disintegrate.
most grubee kits have a metal impregnated exhaust gasket that will last a long time, but usually needs to be grinded abit to match the port.
the head gasket can be reused many times, as long as your careful with it, but if you ever take the jug off, the base gasket will be destroyed.
case gaskets are the same way.
the gaskets on the clutch and magneto covers do no real purpose, except maybe provide a tighter seal, but there's nothing inside to leak out, and unless you submerge your engine, there's nothing that can get inside.
regardless, those gaskets usually last a lifetime of removal.
the gray gasket roll you can get at most auto parts stores works great for intakes, base, and case gaskets.
exhaust gasket material is harder to find, but it's out there.
as for the bolts, i use black allen head socket cap screws for everything. you just need to take out the bolts and the studs and match up the sizes. makes your engine look much cleaner, too.
my problem with the stock hardware is if you remove things a few times, the screw heads will strip out, and the 5 or so different sized flathead screwdrivers i have don't fit them perfectly. maybe i need to buy some chinese ones.
head studs and hardware, i never change. seems to work fine.