I just hit first prestige last night and it seems you retain all your attachments to the guns but they become locked and unlock at their usual respective levels once again. You do receive a permanent unlock token once you prestige meaning you can choose any gun or perk, specialist, scorestreak, equipment etc.. that you can acquire at the very start and retain throughout without having to unlock again. Challenges and camo also remain once you prestige and you gain one extra create a class slot although all your previous custom classes will be wiped.
My advice for your unlock token is choose something essential that you wouldn't receive right from the get-go in the prestige e.g perhaps a gun that unlocks at level 20+. No point in retaining something you can automatically get at level 7 or so.