GPS and fire extinguisher, good advice. Radar probably too, but I think for every ticket I've got, it wouldn't have helped. X-country, they always nail me going to opposite way, and then turn to get me. Ohio once, South Dakota once.
If you do get nailed for a ticket, see what you can do about getting it off the record. Ohio ticket was many, many years ago, and I paid about $100 at a little wood cabin that they called a police station, and that's the last I heard of it. Two years ago, got one in SD, and that's on record, with a bit of a bump in insurance rate.... should be off in another year...
I paid the SD cop $100 right in his car. I thought/hoped it would be like the Ohio experience, but this incident, combined with the insurance hike will cost about roughly $500, maybe more, over three years.
X-country is pretty long and tiring, so good luck with that. 3 days is pretty much the minimum, so I'm glad you have at least one extra day.