Will there be any places to stop and buy drinks and food along the way, and if so, how far apart are they?

You'll want enough drinks and food to get you to your destination and/or reststops, with a little extra in case you're delayed by something like a flat tire. Plus everything you need to fix a flat tire or two, and a multi-tool.

Other than that, same checklist as for any ride -- ID, money, insurance info, sunscreen, lip balm, cue sheet/map/directions, whatever clothes are appropriate for the weather, band-aids, tampons, wet ones, chamois cream...

Also, a song in your heart and a smile on your face.