ffhounddog
Here's the deal. If your coming over as an individual augmentee (not a part of a unit) you'll get an Beretta and/or and M16A2/A4 (you have to bitch and moan to get a rifle, but it can be done). M4s are being fielded to Army units, slow but sure. If you're coming with your unit, you get what you get. Most AF guys have a carbine length rifle with an A2 upper, though I've seen the whole range of things. The contracting guys are buying all kinds of rifle variations because pistols suck in this fight.
I've tried to bolt-on gear with the issue rifle. Back to basics for me -- Holosight and tac light. I put the plastic handguards back on (turned in that heavy aluminum forearm set and bought an aluminim single picitinny rail that goes under the handguard.) I've bought a BUIS (waiting on it to get here) because I can't get one through supply.
After nearly 20 years of doing this, I've learned that KISS applies to anything for SHTF. IMHO -- buy a 16" barrel, a collapsable stock, flat-top rifle and a good optic. You'll be all set then. If you can't get AA batteries for your holosight 552, you've got problems that one rifle won't solve. Don't neglect your magazines. Buy good ones, buy lots of them. Put numbers on them so you can tell them apart. At the first sign of trouble, crush it and throw it away. You'll need a boresnake and a toothbrush to keep the rifle clean. Get something you like to keep your mags in. Eagle molle pouches are great. Functional is better than cool -- KISS.
If you're doing convoy duty, get to know your intel guy real good. Get a brief when you go out, give him a back brief when you get in -- it will help the next guy going out. Know damned sure how to use the radios, where all the camps with gas & medics are located. Get yourself one of the "road atlas" maps from your topo support unit -- they make 'em in theater. GPS works even better with a map.
Don't bring too much stuff -- just the basics. Issue field kit, weapons cleaning gear, swiss army knife or multi-tool, sharpening stone, shortwave radio or .mp3 player, ballistic glasses, and gloves. All that other "tactical" gear just isn't needed and it's more crap you have to keep track of.
Good luck. We're waiting for you to get here.