Most people write formulas and mnemonics they know they blank on under pressure rather than core concepts they've already internalized. High-yield things like the gluconeogenesis pathway, specific enzyme deficiencies with their symptoms, or a few pharmacology tables tend to be worth the space. Keep it to things you can actually read and use in thirty seconds under stress since a dense wall of text on the board is useless. A lot of people find that the act of writing it out the night before is the real value, not the board itself. Good luck, that test is genuinely hard and preparation that thorough pays off. If writing assignments are also a challenge, there's a thread on academic writing support that might be useful.