Base Layers and Backpacks (size) Quailty!!
My favorite category of military surplus, not easy to narrow down. After years in the miltary I like a lot of the gear. ILBE, MREs, and tents. Keep camping and hiking!
My favourite is shelter, tents or something that could be used as one, something I consider to be priority in any situations outdoors. Though it isn't the only thing I look out for when I'm looking for military surplus items.
Clothing most military gear and I have been there is a tough as it gets.