So far, from what I could read online (in this guide and on the wikia, among other sources):
Briefing screen
Pay grade
The pay grade for a mission indicates how much cash players can expect to get out of a mission -- source.
Also this thread suggests it can go up to 10 stars.
Day rate
The dayly income rate is a cash reward with a multiplier for the day a heist takes (e.g. 1x in The Bank Heists and 3x in the Rats Heist) -- source.
Contract pay
The contract payment is a flat amount of cash reward based on the number of white stars (pay grade) -- source.
Payday
The overall payday is the sum of the other two cash rewards (pay grade and contract pay) and will be shown on the map if you select a heist -- source.
Yellow bonuses
These bonuses come directly from the difficulty (or "risk") of the mission, pictured by the yellow skulls on this very same screen. Normal = no skull -- overkill = 3 skulls.
Debriefing screen
Instant cash and bag loot items
The instant cash it the one you loot and put in your pockets directly during the game (jewels, cash bundles, ...) The bags are those heavy packs of money, jewels or even drug you'll have to carry in order to achieve a mission.
Balance
This section contains the sum of all the amounts contained in the Income section ($332,400 in the example given in the question) distributed between two type of accounts: the offshore account and the spending cash.
Offshore account
The offshore account consist of most of the money players steal during the course of their heisting career.
The player has no way of interacting with their offshore account and is only used to show off how much the player has stolen -- source.
Since August 30 2013, you can use your offshore account to directly buy specific missions from Crime.net.
Spending cash
The cash you get, finally. In the given example, it's 10% of the total amount, but so far I couldn't find any precise calculation to know if that percentage can vary or not.
This is the offshore account money and 10% of that becomes you spendable cash. -- source.
Steam user Faildozer has written a very detailed guide, "
PAYDAY 2: The Numbers" ("taken from the game files"). Here is what he has to say about ammo packs, supporting your theory:
The ammo bag starts out with 4 uses, some further info about how usage is counted by the game:
- It's not split between primary and secondary ammo; there's just one pool of ammo that weapons draw from
- How much ammo drawn from the bag is based on a percentage of how much ammo you've used so an empty AK draws just as much as an empty M308 which draws just as much as an empty Crosskill and so on
- A default bag holds enough ammo for exactly 4 full refills (400% ammo if you want to think of it as a percentage)
- The Enforcer skill that increases the capacity of the ammo bag gives you 50% more ammo per bag (so 6 full refills/600% ammo)
- The game will always prioritize filling up your secondary first before your primary, so if both your primary and secondary are completely out of ammo, and the bag has exactly 1 full refill left (or 100% ammo) then your secondary will be refilled completely and your primary will still be empty
Medic bags do get used up after 2 uses (without upgrades). Similar to Left4Dead, you die for good if you go down too often, but healing from a med kit resets this counter. So saving them for teammates that went down multiple times already might be worth it.
Best Answer
In the white xmas heist, it is a random loot in the presents with a super low drop chance.
Buuuut it also appears on the Shoutout raid (the shadow raid's loud counterpart in the murkywater warehouse)
I'm not certain where it is exactly, but it is supposed to be outside the main playing area, near where the trains are at the end of the heist.