Probably the most familiarized way to make fast money is by selling food that you take to your other forest buddy, the bear who adorably refers to you as "Samsquanch". Based on the types of foods and how much you have, you can get some decent coin here.
This is where having a disguise really comes in handy. When you're disguised, you can take food without alerting campers. The only folks that you still need to watch out for are rangers who won't fall for your disguises, unfortunately.
But go to each area and fill up your backpack with as much grub as possible. Then, when it's time to crash for the night, quickly head over to the bear (before you fall asleep) and give him the goods. If you really filled up your backpack, you can easily get 100 or more coins for your efforts.
Get A Job
No, don't worry, I don't mean this in a harsh way, but it's time to get a job and you can do that in Sneaky Sasquatch. You'll need to go get a professional outfit from the store in the town. There's one that's right between the apartments and the arcade.
The basic work outfit will cost you 500 coins but it will be worth it. This is because you'll get hired at the large business building in a hilarious fashion. Starting out, you'll be tasked with delivering mail to your colleagues around the building.
This is an easy job that will net you 200 or coins per day. Eventually, you'll get promoted, and get more coins to build your wealth. I highly recommend using your payday to help pay for an apartment room (if you already have some coins on deck anyway). For the smallest room, it's around 500 coins and then it's 50 per day.
Although that sounds kinda steep, it's not bad once you get the initial fee out of the way. The 50 coins you spend per day will be built back up again quickly by working and doing your usual selling side gig. Also, if you have a shovel, you can find lumps of dirt that reveal sacks of coins as well so you have a chance to be one financially cozy sasquatch over time.
Catch Some (Gold) Fish
In Sneaky Sasquatch, one of the activities you can do is go fishing. Here, don't just catch them and throw them back in the water. You'll meet a fisherman on the other side of the pond (go down the stairs across from the path the leads to the RV park).
He'll give you a fish guide/book that will tell you about the fish you've caught. And when you catch them, you can sell them to the friendly gentleman for some good coin. You easily get double-digit coins per fish, which more than what you would get selling food to the bear.
With that said, definitely keep selling to the bear too when you want to do it. This is just a reminder that fishing can help you rack up some change. Sure, you won't get thousands in just a few minutes, but playing the game regularly and filling up your backpack with fish is a great way to get paid. Just find any kind of water whether it's a pond or the ocean and then pull out that trusty rod of yours.