Re: Brother in Afganistan
Like it's been said, not a whole lot to do with the 249. I had to carry the full-size bitch for a year in Afghanistan myself and then, 2 months before set to return home, we get the tri-rail system and forward pistol grips (which I didn't care for). I begged from day 1 to get a shortened barrel & collapsible stock, but it never happened for me. If he's already got those, that's the biggest thing I could have suggested.
Aside from that, an after-market sling of some sort and an Eotech or something would be great. Also, we had them issued, but I didn't see it mentioned yet; get one of those 100-rnd "nutsack" zipper up ammo pouches to replace the standard 200rnd drum. Especially for just walking around the FOB it's a lot nicer (smaller and half the weight!).
Only other thing I could think of would be an ammo drum pouch of some sort (MOLLE or whatever your favorite system is) if he didn't get any / enough issued depending on how much he's actually patrolling on foot.
As for the bipod... pretty sure you can remove it and the gas cylinder will still go right back in and stay secure without it. With the tri-rail, you could attach whatever bipod you wanted. The one it comes with did feel flimsy (unit broke a couple in training) and they move around quite a bit.
Ask him about the MGO (machine gun optic) as well... he may have had one issued or unit might be able to get one. I never used it, but I heard it's alright (and free). PAQ-4 on the side for nights and you're set.
Edit...
Oh yeah... make sure he has one of those scraper / cleaning tools that is "supposed" to be in the original hand guard. They were like some sort of mythical creature while I was there, "you want a WHAT? hahahah, good luck, they don't even exist!" I dunno, maybe it was just me, but it was pretty useful... most just used their gerber or whateverthehell. (I acquired one)