Law level is naturally a concern, but so are available skills (not everyone has the skills for Combat Armor or plasma guns) and physical stats (encumberance, strength to counteract heft, etc.) Most worlds with any appreciable law level (say, 5+) will take a dim view of people walking around in military grade armor. Even if they are not technically breaking any laws, they're certainly up to no good, from a law enforcement perspective.
And of course you should choose a mustering out weapon or armor that matches your skills. Your Referee might also restrict what hardware you can choose based off of your service, the local Tech Level (for planet-bound careers), or other factors.
My suggestion is to make the Armor be at best Combat Armor (and then only for Marines), and usually Cloth or similar. Much like the way that mustering out with a ship gives you a bare-bones, un-paid for ship, Weapons should also be "stock". If players want more extras, that's why they have money.
Historically under the original Traveller rules, the choices were more clear-cut, since different weapons had Dexterity cutoffs to avoid penalties or gain bonuses when shooting, and the same for strength and melee weapons. Players would scan the weapon list when they rolled a combat skill and pick the choice that best matched their character's stats. If you mustered out with a gun, you'd pick the one that matched your skill. People didn't muster out with armor.