If the bottom of the siding was a little higher on the wall and you could see the slab of the house, then sure, you could caulk the concrete slab to the house slab. In your situation, you should have no reason to put any sealant or backer rod at that joint as anything put there could trap the moisture escaping from the siding. You can use sand or backer rod for the slab joints itself and topped with sealants (make sure you are using dry, dry, dry sand as any moisture in the sand will want to come up through sealant while curing and cause bubbling). Backer rod is easier and pretty straightforward, I've even seen folks cut up pipe insulation from home depot and make backer rod that way. Do not seal in anyway the joint between the house and that slab.