My understanding is that this is 30 minutes worth at 1500 agl, and is the fuel you must have left in the tanks after touchdown.
In my company, as soon as you realise that you may go below this figure, and still be airborne, you have to declare a MAYDAY. It is of course landing weight related.
Any fuel you want to use for anticipated holding should be in the EXTRA field.
Bear in mind you should be able to use the contingency fuel for holding if your burn to the holding point (taxi, climb cruise and descent) is as predicted by the operational flight plan.
Also, depending on company rules, you should be able to anticipate binning your diversion fuel if you meet all the requirements. But Final reserve is just that.