51 items. 2 days 3h 30 min.
Not my best but definitely my favorite explorer of the moment who I like to nick "Mayor" Payne, for obvious reasons...
http://s30.postimg.org/z2moqm3xd/image.jpg
When I beat your record I will let you know
20 guns ( shotguns, laser pistols,some revolvers, rifles, bb-gun mostly common weapons). 2 power armor, 1 legendary dweller (harkness), 1 blue dweller (some lady with fancy dress) and 15 or so other outfits that poor harkness has found. nothing special so far.
I'm only at population 50 or so, but my celeb dweller Moira scored a plasma rifle. That's the most noteworthy loot I've gotten so far.
I had my level 50 Jericho out for two days eight hours, scored a ton of random stuff, plus some focused plasma rifles, and laser gatling, and some power armor. trained his luck up to max now I just sent him out again with the power armor and laser gat and I'm shooting for three or four days. I wanna get the best stuff the game has to offer. lol
I think Luck has a factor in the quality of loot. Despite her previous foray bringing back a plasma rifle, Moira's most recent haul was kinda meh. I have her in the arcade now boosting her luck. I'm putting another dweller through some rigorous training in all the training rooms to get him up to spec for a good wasteland foray too, and that'll also involve some time in the game parlor.
Best item my explorers ever found was a tuned plasma rifle.