Breakdown cover is included with all rentals. They will try upsell to these products:
http://www.alamo.co.uk/HelpfulInformation/740/uk/RSPLUS
http://www.dollar.com/TravelCenter/TravelTools/RoadSafe.aspx
These cost around $5/day, not something I have ever bought or needed, if I had bought it for every rental I have done in the US I would have paid out around $3,000 for nothing.
They also could try sell you personal injury, this should be covered on your
travel insurance.
Satnav is something else they try push, you can buy one at
Walmart for about the same price as 7 days rental.
Other thing they try sell is an upgrade, they will tell you "you have no chance of getting your luggage in the car, you need to upgrade" I once got "the car you have booked is not up to UK safety standards, for the welfare of your family you really need to upgrade"
Basically don't believe a word they say, don't be pressured into anything.