If you've done all that you can do in Rise of the Tomb Raider, you may want to take a look at this DLC that just dropped today. It's called “Endurance Mode,” and essentially adopts the core Minecraft gametype (yep, that game isn't just about building things) — scavenge and craft by day, and survive at night when the enemies come out. The developer is billing it as an “unforgiving” mode, where you need to actually build fires and find fuel to survive, and so on. I can't vouch for it but it sounds cool on paper.
As a reminder, Rise of the Tomb Raider‘s exclusivity is likely going to die off soon with the PC release next month.