Step 1: Get tons of batteries (all your electronic extras will need these things like mad), magazines (yes, really), cleaning tools (don't skimp), lube (apply generous amounts), ammunition (have no fewer than 300 rounds minimum), upper receiver convserions (22lr, 308 win), night sights (trouble happens in the dark), flare launcher (signal trouble), tac light (blinds things and lets you see what you are doing), reflex sight (does not need batteries), and a bayonet (for use as a tool which doubles as a zero ammo force applicator).
Step 2: Practice with the stuff, a lot.
Step 3: keep building you ammo, cleaner, lube, and mag stockpiles.
My personal version of this is:
Get a decent AK, bootlaces, motor oil, a bayonet, and stockpile mags and ammo.