My treasure accounting system is pretty simple:
For my PC, I write any inventory changes on the back of my sheet. For party treasure, I use a seperate sheet.
My notation is pretty simple, I use plus sign and a quantity, followed by the name of the item, to show I added it. I use a - sign to show I removed it. At the end of the game, I add them all up, and adjust my character sheet.
For party loot, I do the same thing, though the difference is, we split the loot at "pausing points" and just cross off the item if it gets handed to somebody.
This +/i/cross method works better than actively marking up the inventory section of a character sheet, which is possible to change a lot during the game.
During a game, my inventory notation space might look like:
-5 SP
+1 shortsword +1
-2 dagger
+1021 GP
This would reflect that I spent 5 silver, got a shortsword +1, lost 2 daggers, got 1,021 GP from party loot. In a real adventure, the list is usually longer.
Since we usually fully split the loot by the end of the game, we don't have a true "party inventory". If we did, I'd keep a seperate document (like the PC's inventory), and still use the inventory scratchpad/notation system to denote changes made during the game, only finalizing them post-game during char sheet update time.
I strongly recommend the notation system for documenting changes during the game. It's pretty simple, and keeps you from pencil marking your sheet to un-readability.
I do the same thing for HP. I'm amazed at players who use sheets with a tiny box for HP, and they constantly erase and re-write the number. It wears out the sheet pretty fast. It's much simpler to use a side column on a scratch paper (back of char sheet even), and just do a running addition/subtraction/total column. Less erasing.
