I can really see any need for a marine to use the inferior las weapons unless they have been fighting so long they are out of ammo and scavengeing weapons also marines dont even blend in with crowds they are over 7 feet tall and built like a brick privy and easily noticed.
As for the gear you can have acsess to only the finest will do for range you have your pick of the godwyn pattern boltgun with a variaty of rounds includeing kraken giveing a longer range and AP, inferno setting the target on fire, hellfire containing mutagenic acid crystals, metal storm proximity amunition, stalker silenced shells, and the armour pierceing vengence rounds ( also possibley even better than a standard RT bolter due to its size), bolt pistol, meltagun, plasmagun, heavy bolter(with surspensors and hellfire rounds), plasma cannon, lascannon, multimelta, flamers, storm bolter and rocket launcher which may contain several different types of missile.
as for CCWs you have you standard list of chain and power weapons from RT as well as a few new ones like the thunder hammer and stom shield but you also have the chapter specific wepons like the frost blades and wolf claws of the space wolves and if a chaplain where to join the squad you could expect a crozius of and if he was a dark angle he may carry the blades of reason.
Grenades should be fairly standard and just lifted from RT
Armour is a really cool subject you may see the astartes scout armour? You will definately see powered armour and there is already artwork for terminator armour aswell so id expect that too. You may also see artificer armour which in addition to the strength bonuses and auto senses of the "standard" marine power armour will be stronger and may contain built in weapon systems like digital lasers or needlers.
peronal field generators may get a look in refractor fields, conversion fields, displacer fields and the more powerfull versions used by the chapters greatest champions may all be made available to a marine that proves himself.
relics of the chapter why not?
Xenos tech? the inquisition can do almost anything they please to keep the imperium safe and if the sanction a brother to use alien weapons or equipment then the marine can.