Anything you delete or simply move to the Trash and empty normally, without using secure empty, is theoretically recoverable. What you are doing when you trash or delete an item is you are removing its known path from the system, but the underlying file is still there potentially recoverable... until it is actually overwritten by new data. You could use erase free space, but I am hesitant to do that myself since there have been glitches and problems associated with that. One is that it may create a huge temporary file which consumes all the free disk space and hangs things up pretty badly.
My best answer, though there may be better ones: AFAIK, the browser history and cache of any browser contain only URLs. The purpose of history is to enable you to locate a previously visited site. The purpose of the cache is to speed loading of previously visited sites. It was probably much more useful when many people had very slow dial-up connections. Now I don't think it much matters. Anyway, I don't think there's any sensitive data recorded in the history or the cache, except if you wouldn't want someone to know which sites you had visited. Many browsers allow "private browsing" to defeat this.
What might potentially be exploited is the form history, where the browser records for future use any phrases, keywords or answers to various fields. Many people recommend turning off AutoFill in Safari. I don't use Safari, but perhaps someone else will know how to find the AutoFill history and maybe selectively delete any previous entries. In Firefox, which I use, there is an Add-on to do this called Form History Control.
From any browser, you would want to remove the following:
|•||Card numbers: Every credit and debit card number|
|•||CVV/CVC: The 3 digit verification codes from the back of several cards|
|•||Social security / national insurance numbers|
|•||Bank accounts: Several bank account numbers and sort codes|
|•||Addresses: Home address, amongst others|
|•||Date of birth: Handy in combination with the above data|
|•||User names: login name for many many websites, even those where I said not to remember the actual passwords|
|•||Phone numbers: my home and mobile phone numbers, amongst others|
|•||Answers to several “security questions” used to reset passwords on sites|