Other protection options may be available (personal accident insurance/personal effects coverage, uninsured/underinsured motorist coverage, etc.), and you may find some of them to represent a value to you, but none of them will be required purchases.

As for USD vs GBP, I'm not sure. You haven't prepaid this reservation? IME, most of these bundled all-inclusive deals are prepaid, but then again, I'm far less familiar with the Budget variant of these kinds of bookings.

If you didn't prepay, I would suspect that the rate loaded in the Budget computers is the USD equivalent of whatever you booked in GBP as of the wholesale (or near-wholesale) exchange rate on the date you made the reservation. The rate is going to be loaded in the computer at the Budget location as a USD rate, and since once the reservation is entered in the system, it isn't touched unless you do something to update the reservation, there's no real way it could be changed to anything different than what it was when you booked it.

You might be able to use this to your advantage by rebooking the reservation if the exchange rate changes; assuming you find the same price in GBP when you attempt a rebooking, if the USD's value has increased relative to the GBP, then the equivalent rate that will be loaded into the US-based reservation system will be lower, since the total in USD has to equal the total in GBP.

Don't take the above as gospel, though; I'm merely speculating based on my experiences with another brand (that very well may do things substantially differently).