4Game

Upgrading your backpack is always worth it if your goal is to make money. Assume a scav bag costs 20k. Assume a trizip costs 50k. You're spending 30k more for 10 more slots. This means if you leave with a full bag (which you should always do, even if it's junk loot) you'd only have to average above 3k roubles per slot to break even. Unless you're stuffing scav guns into your bag this will always pay off.

Let's assume I'm garbage at PVP and only know one map, with a goal of purely ratting around and making money. Avoiding all of the hot spots and good loot areas makes a 40% survival rate a reasonable threshold I think, if not let me know.

This means that 30k you spend per backpack turns into 45k. (Cost multiplied by the number of times you'll have to buy it per raid successful, (30k X 1.5))
This brings the cost per square up to 4.5k. You know what has a higher average per square value? Every lootable object in the game save filing cabinets right now. So even if all I have access to is gym bags and toolboxes, the most common lootable objects in the game, it is still worth it.

In conclusion, if you want to stack more roubles, a bigger backpack is always worth the investment.