Too much to cover, and little you can do about any of it anyway in the short time and limited budget. Knobby tires, straight bars, no racks, heavy pack, 26ers I'm guessing, SPD's?... It won't be fun, but it's doable. As noted, wind is bad. Cold wind is worse. Cold rainy wind is just plain numbing. I hope you have warm weather at least.
So on to some ideas you CAN use. It's a mental excersise in timing. Do the math. 10mph average is pretty doable if no big climbs without downhills. That's only 6 hours in the saddle at a fairly casual pace. I'd ride 2 hours, then rest, maybe 20 minutes or so. Ride 2 more hours and rest a good while, eat lunch, hang out, just chill for an hour. Then ride the last 2 hours and set camp. You'll keep from bonking that way. Keep snacks handy to munch on while riding between breaks. Obviously times aren't set in stone, you know the area, plan breaks around it. Take more breaks for shorter times if you want. Point is, to not hammer the first day out. If you want to hammer, save it for the last half of the last day.
Don't know about your area, but typically you get a lot more sun road riding than mtn biking, so maybe consider sunscreen or something. Might want to pack a little baby powder. Saddle sores are more prevalent in roading, since you're basically just sitting all day and cranking. Not like the body balance workout of technical off road stuff. Definitely use the bottle cages and don't backpack water. Bag on the bars has already been mentioned, just check all your cables when you crank the bars, so nothing binds up when you turn. Oh, and lock out your forks on the climbs if you have that option. You'll notice the bob a lot more on road.
Wear something bright. Use a blinky if you can get one. Common sense stuff I guess, but easy to forget if you just single track or off road.
Just pace yourself. No hurry, it's only 60 miles and you've got all day long to do it. Besides, how hard can it be? You're sitting down while doing it! You may be telling yourself one of these things before you get back home, but you're young, you'll be fine. Good luck!