ALL Students should have:  Music stand, tuner and metronome (check out metranomeonline.com).  At the high school level most students are ready to play on a professional quality instrument.  If a students has been using a rental instrument for the past several years, now is a good time to invest in purchasing a quality instrument.  If student already has purchased an instrument then it may be time to upgrade the mouthpiece/switch to the next reed strength. 

For clarinet and saxophone players:  Vandoren reeds (if you're switching from Rico's use the same strength because Vandoren's are harder).  As far as mouthpieces go, the best thing for individual students to do is to try them.  I've had students sound great on a mouthpiece that I don't normally recommend.  For clarinetists, I recommend the Vandoren B45.  Selmer, Vandoren are excellent quality saxophone mouthpieces for a traditional concert band sound. 

Every brass player must furnish his/her own valve oil and slide grease.
Every woodwind player should provide his/her own cork grease.
All percussionists must furnish their own sticks and mallets.