A suitable backpack such as Macpac Rapaki 28+ with a Dyneema Polyethylene Level III 10x12 Ballistic Plate stored inside should give you some protection in this scenario. A fixed blade knife such as a Fairbairn-Sykes fighting knife and a Mk9 Thunderflash could be useful especially if you can get within 20 feet. All bets would be off. A Fritz helmet would be ideal but would be a little inconspicuous when being worn to lectures.