Get yourself a Carinthia Defence 4, it's the current Army issue bag and a fantastic piece of kit (says me having just spent last night in one when it was well below freezing and had to chip ice from the tent in the morning and was toasty throughout ), the stuff sack will compress it a good way, the shell is waterproof but not taped, and it is available on eBay from around £50 if you're lucky
He either fears his fate too much,
Or his deserts are small,
Who dares not put it to the touch,
To win or lose it all.