This is, to no surprise, harder than it sounds when first playing Interloper.
You start with barely any gear or clothing and the weather is frigid, so finding an indoor location is the first thing you need to do.
The best spawn is Forlorn Muskeg as it connects to the easiest region Mystery Lake (there are also cat tails on the way giving you some calories) . As soon as you make it to Mystery lake make a B-line to the Trapper's Homestead, it's one of the few places on the island that have a natural above 0oC interior. There is also a chance for matches to spawn there allowing you get water as well. If there are no matches, warm up, loot the homestead and try and make your way to the camp office for more supplies, you will usually find at least some sort of drink between those two locations, and if not, try your luck at the lake cabins.
Interloper difficulty in a nutshell:
You will never spawn in beginner regions (like Mystery Lake), Always spawn outside and have the chance of spawning at night as well. You also don't start with any matches and they are rare find on top of that. You rarely find anything in containers and a few cargo containers on Timberwolf mountain don't spawn and the ones that do have drastically lower quality items in them. There are no firearms, bows, hatches or knives either, you have to make them yourself. A fun but difficult challenge.