Mystery Lake is a good location for collecting supplies due to the abundance of cabin and huts around the lake.
A Camp Office is located at the north-western tip of the lake between the lake and the rail road tracks, this building has an abundance of supplies and is a contender for one of the best base locations in the region.
There are two collections of lake cabins on the south and south-eastern end of the lake, usually one cabin out of each collection is burnt down, but there is still a large amount of supplies to be found in each.
Further up past the triple lake cabins a Lone Lake Cabin quietly sits abandoned.
There is the occasional wolf (usually two or 4) as well as a bear on the lake which makes exploring slightly risky sometimes. You can harvest the cattails from lake edge as a food and tinder source. Several fishing huts (each with a stove, cupboard and fishing hole) are scattered over the frozen lake and a small strip of land sits in the middle of the lake. Over all Mystery Lake is a great location for supplies. A Rifle may spawn near a corpse behing Lone Lake Cabin.