I dont drink alcohol at all while I am driving over there but I usually have 1 Vodka with the meal on the plane as it is still roughly 6 - 7 hours out from Florida plus say another hour before I get behind the wheel of the hire car.
Yes, I forgot to add an hour to 90 miniutes to clear passport control, collect luggage and then walk out to the hire car area, and then stand in line before finally walking out and loading luggage in the hire car.
My advice is to have a drink early on the flight, no more than 3 units so a good double whisky, or 3 small glasses of wine with the meal and thereafter either sleep or switch to rehydration mode by drinking soft drinks, water, or I find tea helps (yes I know about caffeine being said to dehydrate but I an not convinced)
Plan your route to your hotel before hand and write down the road junctions, number and direction changes beforehand. If landing at night at Sanford, most road signs will take you down the toll road and at night not all toll booths are manned so have change in quarters and half dollars.
It is possible to to get from Sanford to Orlando and Kissimmee via the I4 but you will need to plan how to find it.
Car hire pick up and luggage collection seems much faster at Sanford than Orlando Int, mainly because they have a single stage luggage pick up process and are geared for moving British tourists through the system from charter flights.
Orlando Int is however about 30 minutes drive time nearer to all the activities and it is pretty hard to go wrong finding your way into Orlando and Kissimee
Always ask for a free map when you pick up your hire car, but as soon as you get to a gas station, I would buy an American Automobile Association folding map of either Florida or just Centrel Florida depending on your plans.
Lastly, If you can split your hire cars keys easily, do so. Have the two keys carried by different adults, if you lose your key, the cost to get a man out to make a new one and then programme it to work with your immobiliser can cost up to $300. If you cant split them, then attach a good solid dog clip and always clip inside pants, bumbag or rucksack. I have seen quite a few families stood in the WDW parking lot, waiting for the man to come out and do the key thing. It is real easy to lose keys on coasters and when you are in and out of a sack or bag during days in the parks.
Oh, and have a small flashlight with you. Invaluable if you are landing at night , you will need to find all the car controls and seat adjustment switches ( a lot of the bigger cars have all electric seats)