I made my first own character sheet yesterday, and having used them in our campaign today, one element I included already proved to be really quite useful. What I did with the space for inventory was to split it into two tables. One for items worn on the body, and a separate one for items in the backpack.
The reason for this is simple: If you are using Encumbrance in your game (and I recommend taking a look at this very practical system to manage it), players have many reasons to consider leaving behind most of their gear in a camp or with followers to explore and fight without being encumbred. It’s particularly useful for thieves, who often need to have no encumbrance at all to use their abilities and rarely have high strength, but can also become very relevant if the PCs have already collected a lot heavy treasure that could weigh them down considerably.
By making the content of the backpack a separate table from the rest of the inventory and writing down the total amount of load for each, it becomes a lot easier to see what difference it makes when the backpack is dropped. It seems obvious to me now, but I think all character sheets should structure their inventory this way.
I also made separate boxes for coins that are carried in a coinpurse on the character, in the backpack, or stored in a vault at a home base. In most games, characters can become ludicrously rich, and it would be nonsense to carry around hundreds if not thousands of kilos of gold and silver all the time. Also, it’s less painful when the characters happen to get robbed or lose all of their gear. (And allows for NPC burglarizing the PCs home while they are away.)