@GreenGrenade The answer depends on what you want or do not want him to know, as well as how old and how long Gareth has owned each particular item. When he's concentrating, or just paying attention to a certain point, Lucas can pick up a fair amount of implied facts, but not always actual facts. For instance, someone shouting might usually mean anger, and if he doesn't manage to catch the words or the rest of the conversation, that's probably what he'd assume, but it could also just mean someone forgot something and the person's trying to let them know, or any number of other reasons to shout. Except to be heard over noisy things, cuz he'd probably be hearing the noise, too. :P
Most things that are on or always near a person, Lucas tends to assign some importance to, unless it's clothing. Simply because that's the general method of dealing with things someone thinks are important, they keep them close. (barring things inconvenient to carry around and very valuable items)
After reading Gareth's sheet, my best guess is that he'd seem like a steady, solid individual, as his clothes wouldn't be chockfull of every emotion under the sun, but would reflect a certain calm. But also someone he might be afraid of getting angry. It depends on which clothes he happens to have with him, and how much his anger is fuelling his Mindjack persona, because a spike of anger would be more disconcerting than a steady irritation and the combination of Mindjack emotions with civilian emotions would be confusing. There's also the matter of that gun, and how often Gareth has been in the line of fire in those clothes. As Lucas could pick up on the noise and heat of the gun's use, and potentially the rapid motion of air over the clothes(though he might just put that down as maybe he lives in a windy place, unless he focused on it more intently). He'd be able to tell that Gareth is, at very the least, a man of action, as his hands probably do not shake when he holds that gun.
He'd probably be able to pick out his name, and the names of a few other people, most likely Leah and Danny, though placing their relationship would be harder.
The picture, without actively seeing what it is and what it's depicting, would mostly come across as a well-liked piece of paper. As I'm assuming he hasn't folded it, Lucas could hazard a guess that it's a picture(particularly if it's old and before the time of digital printing, then he'd have the dark room process to go off of), but it could be a postcard, even without being written on. If he saw it was a woman he'd probably assume she's family. And he might, but only might, say she's Leah, most especially if Gareth ever says her name while looking at it.
He might hear some of the conversations Gareth had with Danny concerning his recent actions, and if any of the clothes are what he was wearing when he learned of Leah's death, touching them would probably tell Lucas that there is heavy loss in Gareth's life, and he's still feeling it, to some extent.
And the bag itself might well tell him how well-travelled Gareth is or isn't.
It generally takes him a bit of time to officially assimilate all the little hints and clues and assumptions into an impression that he can articulate and reason out. Right off the bat though, he'd accept Gareth as a calm, but potentially dangerous person.