There are a bunch of stuff you need/want to have to maximize your money-making efficiency, but it will still work if you don't have them all at the beginning.
Just take your time, enjoy the game and you will have everything eventually.

1. A functional car - a van (20 cargo slots)
   OR ideally, a flat-bed cargo truck (35 cargo slots)
   
   
2. Cash - ideally $800,000, but this method will work with less
   If you are totally broke, i.e. you just started a new game, go to Method 2
   
   
3. Access to Dmitry "Oligarch" vendor/shop
   OR Ideally Stantion control point owned for your peace of mind
   
   
4. Military Base control point owned

Here is how it works. The Gas Station produces gasoline for selling (on-site or at vendors) or transporting to the next point for production boost (for which you will also get money).

• Normally, the base sell price for gasoline is $50/unit at any vendor.
  
• For selling at a control point laptop, you get a +33% bonus, at $66/unit.
  
• For transporting to the next production point, it gets sold at 12x base price, at $600/unit.

Dmitry "Oligarch" at Stantion sells gasoline/fuel for $10000 per 50 units, that is $200/unit.




Now the math starts to add up, isn't it?
Not counting the fuel spent on the road, if you buy from Dmitry, move it to receiving point, you will earn $400/unit. Each stack is 100 unit, that is $40000 per slot of storage.

You just need a receiving sector - Military Base, and a way to move large volumes at once (if you value your time). Obviously it will work with other cars and smaller backpack, but to be efficient - a flat-bed cargo truck has 34 slots for gasoline minus the car battery, and whatever you can carry on your backpack.
If you have the cash, just load up as much as you can afford - in this screenshot, buying costed me ~$800000.




Finally, move it to the military base to get your payout.
Each run pays ~$1,540,000 after deducting the costs of buying and transportation.
Remember to keep a bit of fuel left for the return trip to Stantion.




As a bonus, you should also pick up the 12 boxes of weapons from the Military Base, and move it downstream to Stantion for $180000. But it's a drop in the bucket compared to what you get moving gasoline.

There is luckily a 2nd method if you are broke or cannot take advantage of the first method for whatever reason.

Similar to gasoline/fuel, wood is also an abundant resource that is very easy to find. In fact, usually there is 20-30 units of wood next to the furnace in every shop, which surprisingly, also fetches a good price. It is also worth mentioning that the City control point produces wood quickly, at least much quicker than other resources like gasoline.

The best part about wood - you already start with an axe, so just take over the Sawmill, get any car running, chop down trees around it, and sell them immediately.