I keep: a few patches, front sight adj. tool, jag/punch, bore and chamber brushes, stripper clip loader, ear plugs and various springs in mine.

What should be mandatory? When I have the cash, I'll throw a spare bolt in the grip.

Just put a G.I. cleaning kit in the butt. Put your ear plugs, an extractor and spring in the pistol grip if you have to put something in it. Front sight adjustment tool? Isn't that why bullets are pointy? Clip guide? That should be in each bandoleer. Don't waste the cash/space on a spare bolt, your not going to need it, ever. Everything else is for cleaning. Don't waste your energy planning for emergencies that will never happen. Mandatory? A complete buttstock cleaning kit, for emergencies only, period.

recently bought a bushmaster upper, bullet will not adjust front site,,tight as hell,,and no room for bullet to get a grip,,hope this is not a problem with BM front sites,, my colt front site was adjustable with a bullet,fmj

Batteries for the Comp M and a roll of $100 bills to buy more ammo.

No really:
Comp M Battery
World's Fastest Gun Cleaner
1 oz bottle of CLP
Firing pin
Firing pin retaining pin (Lord I hate those!)
EAR plugs

I would also like to add to Paul's suggestions:
an extractor, the little spring & rubber the little "dealie" that goes with it.  A cam pin & the cotter pin(because I have heard they lost easily).