Unfortunately, critical successes in this system really only helps the group generate AP, they don't really technically have another benefit.
@Squadfather, if you would like to spend a luck point, see the ways to use them
here. The uses that could apply here are
Miss Fortune and
Luck of the Draw. So you could reroll the dice I used to figure out what you were able to scavenge using Miss Fortune, or come up with something completely new to add to what you guys find in the barn using Luck of the Draw. The 2d20 system, from what I can tell, is a much more narrative and flexible system than say, D&D5e. There are no clear cut rules for what can and cannot be added to the scene using luck points, so feel free to be creative or brave! I can always veto a suggestion for what you find, so don't be worried about overstepping or anything. Obviosuly you're not gonna find a whole suit of power armor just by spending a luck point, but perhaps another clue to why he was crazy and off his rocker, or just some extra ammo or a stimpack.
(I don't have anything else planned for the barn, so it's not that I am hiding clues behind the spending of luck points, just FYI)