Hi,
Most of the hats and body items are from Team Fortress 2 with a few of them from other games such as Portal. Luckily Team Fortress 2 is free on steam so you'll just need to download it and run it once to make sure it's mounted to Garry's Mod.
I can't confirm if the glow on the loot in Sanctuary is also used from TF2 but try the above and see if that helps. If not, feel free to come back and reply here then we can try and help you further