Even if your wife's will says you inherit everything in her estate, that may not mean that you inherit all her assets. Her bank accounts may go to you, or they may go to someone else whose name is on the account. Your rights to the money vary according to the circumstances and your wife's wishes.
Payable on Death
If your wife set up a payable-on-death or transfer-on-death account, the contents of the account go to whomever she names as beneficiary. All the beneficiary has to do is present a death certificate to claim the account contents. When you live in a community property state, however, you have a right to half of what your wife earns during marriage. Even if you're not the beneficiary, you may have a claim on at least half the money, if your wife opened the account during your marriage and it contained marital funds.
With a joint account, your access to the money depends on whether you're the co-owner. If you are, it's simple: in almost all cases, you have the right to everything in the account. If it's someone else, and the account has a "right of survivorship," then that co-owner gets the cash. When the account doesn't have a right of survivorship, your wife's share of the account passes to whomever she named in her will, whether it's you or someone else.
Just One Name
If your wife's name is the only one on the account and there's no POD beneficiary, the money goes to whomever she names in her will. If she doesn't have a will, your state law spells out how to divide her assets. Typically, as the husband, you get the largest share of everything she owned. If she made a will that gives all her assets to someone else, in most states that's invalid. If that's the case, you can ask the probate court to override the will to cut you in.
When setting up a joint account, your wife should review the paperwork. Many banks automatically assign co-owners a right of survivorship, while others never do that unless specifically asked. If your wife has a preference, she needs to tell the bank. Your wife should also update any POD beneficiaries as her life changes. If she leaves an ex-husband's name on the account, for example, some states will honor that even after she marries you.