Is it possible to copy my Steam copy of GTA V to my non-system Samsung 850 EVO SSD, which I have a SATA to USB 3.0 adapter for (so essentially a fast flash drive in my case), and play said game on a different PC with no Steam installed on it by starting GTAVLauncher.exe or something? Even if it's just single player? If so, how would I do something like this?
Yes, you can do this. Copy your entire Steam directory from your PC to the SSD, except for games in the
steam\steamapps\common folder that aren't Grand Theft Auto V. The Steam install directory is usually
C:\Program Files (x86)\Steam. I'd recommend copying it to the root directory of your SSD, so the copy becomes something like
Then on your other computer connect the SSD and start Steam by running
steam.exe on the SSD, which should be something like
D:\Steam\steam.exe. Running the client like this will cause it to install itself on the other PC. After that's done you'll be asked to log in like normal. Then find GTA V in your list of games and then "install" it. Steam should find the files that you've already copied to the SSD, and not have to actually download anything.
If does have download something, don't panic. It'll probably say something like 0/50GB but it's probably only needs a couple files. If you pause and restart the download it should change to something like 49GB/50GB.
After the "install" is done, it should launch the game and it should play fine.
Note that if you move the SSD to yet another machine you'll have to go through this again. And if then you move back to the second PC you'll probably have to through it all again on that PC as well. So it's probably not as portable as you were hoping, but it should at least save you from having to download GTA V multiple times.
You need to have Steam installed and be signed in on a Steam account that has GTA V in order to launch and play the Steam version of GTA V. The type of the drive the game is on doesn't really matter in most cases as long as it has enough space for the game itself.
Steam on the other computer(s) likely won't know it's installed already when you first try to play it, so you'll have to make Steam detect the game files.