So I made a cheat sheet of the player-facing rules I'm using from DF16 for my DF Lost City game.
That way, my players are looking at the exact rules I am, and can prepare appropriately. After all, the characters can sense tiredness or know how hot they are or experience the jungle, but the players can only make decisions based on descriptions and roll mods. I'll describe as I go, but I wanted to put the roll mods in front of them so they can make informed decisions.
(In game, the characters will have put up with this crud on the way to the starting point, so they'll be experienced with it. This helps explain why their loadouts reflect the area so well.)
Vic suggested people would like to see it. I think this is true, but it's mostly from DF16 so I can't just cut-and-paste-and-post what I largely cut-and-pasted. It's stuff that is in DF16. But what stuff?
Here it is!
Movement and Travel Time as written, from p. 23. We don't using Hiking skill but successful Navigation will keep you on the x0.4 trail instead of the x0.2 jungle. Sometimes, "I'm pretty sure it's the right fork" and being wrong means backtracking!
Nasty Weather is from p. 30-31, but I simplified Weather Sense down to mitigating the effects because you do some unspecific "preparations" and "adjustments." Why don't you do them all the time? Because it'll slow you down even when the weather is good.
Camping, p. 24-25, as written. Actually I didn't put these on the cheat sheet as people have them down by now. Everyone say it with me, success means pick two!
Scouting, from p. 25, as written.
Heat and FP, from Harsh Climates, p. 30 and Travel Fatigue, p. 24. I adjusted the +1 FP for "plate" to "metal armor" because GURPS is extremely generous about armor worn in heat. The daily Survival roll is at -2, net, for conditions and temperature.
It's a trek to a known destination, not an exploration, so those and some random encounters with bad conditions and trail problems as well as biting flies and jungle leaping leeches and the dreaded tree lobster is really what it's all about. These ensure being heavily equipped and under-prepared suck, but also ensure being prepared means you know, in game, what you're getting for giving up DR and heavy but useful gear.