There are numerous codes used in box 14, often by different states and local taxing authorities, too many to include in the drop down menu. So, you should choose "other" at the bottom of the list if your code is not listed. The codes can be helpful to inform the tax filer of the purpose for items listed elsewhere on your W-2 form, but they normally have no direct affect on the entries in your tax return.
So, it is probably not critical what code you enter there unless it matches one of the codes TurboTax lists. It may helpful for you to understand what is being reported on your W-2 as you may need that to answer questions elsewhere in the program, so you may want to ask your employer about them if you are unsure.
In your case, RET may stand for retirement plan. CAF may stand for cafeteria plan. In that case, they may indicate that you have untaxed income used for both of those benefits, which would be reflected in box 1 on your W-2 form. Your wage income may not be including those benefits as taxable income.