If all of the filters have been done before the trip then I would just carry a quart of 5W40 full synthetic, your choice of supplier. An additive of some sort, Primrose etc would be good as well. Since we are heading into fall and you are coming to Chicago I would pick up some winter additive when you are up here. It prevents gelling of the fuel at low temperatures and you know you are going to pick up a tank of summer diesel somewhere, sods law says it will be the evening you get a rare frost outside your hotel! It is also good to add to your tank before you hit the mountains or go skiing. I use Kleen-Flo Low Sulphur Power additive, it improves your Cetane level and add lube for your fuel pump as well as anti-gelling agent. It can't hurt to have relay 109 which is the main power for glow plugs etc as well, a $25 part. I also pick up a box of 100 latex gloves that I keep in the trunk, cheap and good to use if the station looks skanky or you have to play with your fuel filter to drain out the water you picked up at the skanky station!
I would also look at picking up a set of metric tools in Chicago, why haul all that weight out here. Just your basic trunk set in a plastic case, with a couple of Torx drivers -T20 and T25 to do the ventectomy on your fuel filler. A good tire gauge wouldn't hurt. I just drove across this summer and averaged 56.6 mpg IMP which would be around 48 mpg USG, the whole trip from Ottawa to Victoria via Yellowstone Park took me 7000 Km or around 4500 miles and cost $200 USD, your distance would be shorter but the cost of diesel has gone up from the average $2.30 per gallon that I paid. Oh and bring your favourite CDs as it helps to pass the time, you won't be stopping much as you only have to refuel every 10 hours of so.....
