• After moving to a new area on the map, your companion will switch to their default weapon. Which means whatever weapon you give to them WILL DISAPPEAR FOREVER. Don’t be surprised if you find your treasured weapons disappearing one by one, not your fault. (Well, not your character’s fault, but you as a player)
  
  This is me and my meat shield.
  Here, I gave my companion my beloved kitchen knife
  I moved to a new area on map, and my kitchen knife was lost forever. My companion magically switched back to his scoped rifle while I was still holding the one that he gave me in the previous area. Generally speaking you can get infinite rifles using this glitch but you can't sell them so don't bother.
  
  

• There’s a special area called Whistler's Forest which is located on the left of the starting area. It has the danger level of 10, which is pretty high for a beginner and you may not consider going there just yet.
  However, if you don’t go there when you first have the chance, that area will be locked for the remainder of the whole playthrough (reasons unknow). This area has some interesting stories, very good loots and weapons as well as a few more locks/notes for the achievement persuaders.
  Note that once you entered that area, it will be permanently unlocked for the remainder of this playthrough. You don't need to worry about not having the chance to revisit this cursed forest.

This is my first playthrough where I didn't enter the Forest at first chance cuz I thought I could level up a bit then come back with better equipment. But as you can see in this screenshot, the Forest area is no longer available and is not even visible.

• [TL;DR: if you don’t care about all achievement as well as a few extra exp, skip this one]
  Try not to get your security level TOO high. As a matter of fact, I don't suggest you give points to that skill at all. If you are very good at security, one of the in-game achievements can be rendered impossible: Force open a lock which has only 30% chance of success. If you get your security level above 30 or so, every normal/hard lock you come across will have a force chance of at least 40% or more. As mentioned in another Steam guide, you only need 20 to crack open hard locks. And 50 for a very hard locks which is the hardest one.
  (I think I only met one or two VH locks during one of my single playthroughs.)
  
  For the same reason, you should be somewhat calculated when reading books that give you security points. This is probably the worst skill in this game. Once you managed to get that 30% achievement, you can read as many security books as you want. I'd keep it at 10-20 at early playthrough.

• [TL;DR: if you don’t care about non-rewarding side-quests, skip this one]
  Don’t throw away all the junks and broken weapons just yet, some of the tasks may actually ask you to get them (Side notes: the rewards are crappy). These stuffs won’t just pop up once you actually start looking for them. Some of them can be randomly dropped and some of them have fixed spawn points. I doubt the fixed ones. like the broken board, are able to drop randomly as I never found a second one in my single playthrough. The thing is that you are very likely to drop&destory them when you first pick them up and the task will be given to you after you lose them. This might be a bit spoiler but trust me you will thank me later. You will only need to keep one of each:
  
  •Broken Board
  •Metal Sheeting
  •Paper Weight
  •PPM 9 Pistol (original one)
  •Roll of Tape
  •Welding Rods
  
  And two for each:
  
  •Bag of Nails
  •Broken Pipe

• Exceeded exp will NOT pass to the next level. You will waste a lot of exp if you’re not careful with your achievements. Assuming you are 500 exp away from next level and you get an achievement that rewards you 10k, you will end up losing 9.5k exp. Three of the infamous examples are:
  The 2.5k which is granted when you level up a skill to 50.
  The 10k which is granted when you level up a skill to 100.
  "Death from above"
  
  This is a perfect example where I started at level one. I only need 100 exp to level up.
  
  I fly-dropped a zombie, gaining 500 exp as I finished a secret achievement.
  
  And yet I'm still at level 2, which required 400 exp to level up. To make it worse, I started level two with 0 exp. Just like every level after that.
  

• [TL;DR: ignore this if you don’t persuade exp very much]
  Grinding too much exp in a single area, you’re probably gonna hit the level cap and regret doing that soon. The level cap is 5 levels above the danger level. Meaning if you reached level 6 at a zone that has danger level of 1, you won’t receive any combat exp after that.
  
  
  In worst case scenario where you haven’t complete the main quest in that area at this point, expect to tolerate “no XP, enemy level too low” for some time. Looting/Achievement/Task exp still grants as always.

• Hardcore is not the mode which you lose your save file if you die. You can actually reload back to your story where you will be revived in the same room where you got yourself killed. You get to keep everything like nothing happened. Well, something did happen and you will face the following (ignorable) penalties:
  HP down to your roughly 1/3
  Food down to 30%
  Sleep down to 30%
  These kind of penalties are something that can be painful only when you’re having a fresh start.
  
  I die
  
  I LIVE
  
  No wait...
  

Don’t bother finding secret achievements online. Some of them are actually story-related that you can’t miss. I blocked these ones in case you actually give a damn about the story.

I tried as hard as I could getting all of them in one go. But as you can see, it is nearly impossible. Especially for the ones that are related to the lockpicking / lockforcing. There are simply not enough locks in the world for you to pick/force. It might because of my carelessness, but I was barely able to force 1 or 2 locks after getting the 20-lockpicking achievement before I finish the game.

Last Stand Union City OC: Kervin
by Ratwo619.
https://www.deviantart.com/ratwo619/art/Last-Stand-Union-City-OC-Kervin-892412814