Locked vehicles, safes, currency and a lot more.
The currency isn't bad in itself, its just too many types and then people add in Gems too so its how many obsidian for a gold bar and silver and briefcases? and a ruby is worth how much? Need a damn cheat sheet printed out. Currency would be good with a single type.
Locked safes .. not bad idea if they are rare and can be blown up with explosives.
The base building in Epoch is tedious ... as is having 18 ingredients to build in Overwatch. The current base building for Dayz is superior IMHO though. What I actually
wanted to implement was something like is in Wasteland. You drive your truck up to the building supply trader and buy "building X". It spawns in the yard and you have to place it into your vehicle. Something large requires a large vehicle (Ural, V3S etc). Now you drive to your base location, and unload the item and place it on the ground. For more realism you would also have to drive into a city and hire some ai workers to come and build the item for you at your base so you get your new barn, house or wall tomorrow, not immediately. (I had already developed a system of hiring AI as drivers, bodyguards or companions etc. ).
so what I am saying is there is benefits to all the systems but it depends on how they are implemented as each can be made too easy, too difficult or just too confusing.
But to choose between Overwatch and Epoch comes to this:
*Do you want weapons and vehicles that are different from the default available in Arma2/Dayz? If so then choose Overwatch. I think there are actually TOO many different weapons in overwatch although some have said that adds to the game. There are maybe 20? additional pistols which require different ammo. So players can find a cool pistol/rifle but then they have to search for the ammo for it. There is a handful of different ammo for the 20 or so additional rifles. I don't count the 100 variations of the ACR as separate because they are the same rifle with varying color/sight/accessories ... still the same weapon.
*Do you want a system of building and buying weapons, vehicles, supplies rather than searching for them? then choose epoch. Epoch reduces the need to scavenge everything and search for the item you need. Its supposed to be a more 'civilized' Dayz. People are more likely to focus on building larger bases so Epoch might promote more PvE and less PvP.
Myself, I started with Dayz, moved to Overwatch because of additional weapons and vehicles then moved to Epoch because it has all the default Arma2 stuff unbanned. I dislike epochs method of spawning vehicles randomly, I want to put spawn locations where I want them to be found at. I was happy with Epoch once I removed most of the traders and placed the remaining ones at proper locations. The building system is
okay as it is, not perfect but better than nothing. There are several things I really liked in Overwatch and would like to have in Epoch: the Raven (nobody ever uses it but its cool). The Mozzie gyrocopter, it LOOKS like it belongs in post-apocalyptic society. The Taser .. nothing like tasing a player in the store and stealing their stuff. What I did do was add the Raven mod and if players wanted to download it from my website then they would have access to it. All the players without the raven files could not see the items spawned nor the Raven in flight which was no big deal.