Excess gold and valuables not carried by the PC must be stored in the bank, unless they have property in which they feel secure storing their valuables.
Storing gold: The bank requires a 10% cut for any gold stored. The 10% counts towards XP gain. This is charged only once per deposit.
Example 1 - depositing wealth: Barbara the giant woman wants to deposit 420 gp worth of valuables to the bank. Barbara's bank already has 666 gp stored. To deposit the 420 gp it costs Barbara a one-time fee of 42 gp.
Storing items: May be done by purchasing a bank lockbox for a one-time fee of 100 gp. A lockbox can store 5 slots worth of items and will always remain available to the PC. Any number of bank lockboxes can be purchased.
Example 2 - depositing items: Barbara the giant woman also has a two-handed sword they don't want to risk misplacing while carousing. Barbara does not already have a bank lockbox and pays the bank a one-time fee of 100 gp to purchase one. Storing the two-handed sword (3 slots) leaves 2 slots remaining in the lockbox to be used.
Note: Not storing gold or other valuables at a bank makes it more susceptible to potential loss during carousing!