from my somewhat limited expirience, i would say, ativan, just in case (to help aid sleep when youre ready, or if youre seriously freaking out and cant stop), a safehouse, a StringN'It, glowsticks, gum, good music, a good friend youre comfortable with, a nice blanket, gatorade, orange juice (not for the vitamin c, but bc its like liquid food if you cant get anything solid down), keep your cell off, someone capable of driving in case you need to exit, something you can play with (if you get anxious, it helps to have something to do with your hands), and i agree, a note or someone with you to remind you that youre tripping, youll come out of it eventually, its okay. also, keep in mind that any bad situation you get into inside your own mind you can talk yourself out of.
oh, and please, do not listen to jack johnson (musician, artist, whatever he calls himself) bc he ruined what should have been a nice time for me. there is nothing worse than jack johnson on repeat while ur tripping.
have fun! : )