Free plain fries per burger purchase Offer valid: Monday – Sunday One valid UNIDAYS student photo ID must be shown to the teams at time of order – quoting Unidays Discount cannot be used in conjunction with any other vouchers or other in-Shack promotions Offer claimed at cashier till only. Only available for dine-in or takeaway only. Not available on delivery. Available at all UK Shake Shack (except airport locations – not available at Gatwick Airport)